Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.44   11.771%   $260.9182   $260.92   $260.90   $260.90  
  Purchase #2 $174.54   13.239%   $197.6474   $197.65   $197.65   $197.60  
  Purchase #3 $138.52   12.484%   $155.8128   $155.81   $155.80   $155.80  
  Purchase #4 $127.92   13.604%   $145.3222   $145.32   $145.30   $145.30  
  Purchase #5 $247.78   13.259%   $280.6332   $280.63   $280.65   $280.60  
  Purchase #6 $218.92   9.245%   $239.1592   $239.16   $239.15   $239.20  
  Purchase #7 $235.36   5.528%   $248.3707   $248.37   $248.35   $248.40  
  7 purchase totals = $1,376.48       $1,527.8637   $1,527.86   $1,527.80   $1,527.80