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 $223.36   7.146%   $239.3213   $239.32   $239.30   $239.30  
  Purchase #2 $235.80   11.497%   $262.9099   $262.91   $262.90   $262.90  
  Purchase #3 $42.52   4.836%   $44.5763   $44.58   $44.60   $44.60  
  Purchase #4 $74.64   3.747%   $77.4368   $77.44   $77.45   $77.40  
  Purchase #5 $120.29   10.739%   $133.2079   $133.21   $133.20   $133.20  
  Purchase #6 $176.29   6.785%   $188.2513   $188.25   $188.25   $188.30  
  Purchase #7 $119.69   9.164%   $130.6584   $130.66   $130.65   $130.70  
  7 purchase totals = $992.59       $1,076.3619   $1,076.37   $1,076.35   $1,076.40