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 $88.55   10.341%   $97.707   $97.71   $97.70   $97.70  
  Purchase #2 $238.93   6.807%   $255.194   $255.19   $255.20   $255.20  
  Purchase #3 $223.72   3.758%   $232.1274   $232.13   $232.15   $232.10  
  Purchase #4 $22.53   4.417%   $23.5252   $23.53   $23.55   $23.50  
  Purchase #5 $185.48   10.728%   $205.3783   $205.38   $205.40   $205.40  
  Purchase #6 $150.40   9.631%   $164.885   $164.89   $164.90   $164.90  
  Purchase #7 $60.98   8.324%   $66.056   $66.06   $66.05   $66.10  
  7 purchase totals = $970.59       $1,044.8729   $1,044.89   $1,044.95   $1,044.90