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 $137.44   11.528%   $153.2841   $153.28   $153.30   $153.30  
  Purchase #2 $246.78   9.217%   $269.5257   $269.53   $269.55   $269.50  
  Purchase #3 $51.92   12.692%   $58.5097   $58.51   $58.50   $58.50  
  Purchase #4 $133.68   9.117%   $145.8676   $145.87   $145.85   $145.90  
  Purchase #5 $104.99   6.220%   $111.5204   $111.52   $111.50   $111.50  
  Purchase #6 $163.29   8.809%   $177.6742   $177.67   $177.65   $177.70  
  Purchase #7 $136.44   12.583%   $153.6082   $153.61   $153.60   $153.60  
  7 purchase totals = $974.54       $1,069.9899   $1,069.99   $1,069.95   $1,070.00