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 $86.49   13.452%   $98.1246   $98.12   $98.10   $98.10  
  Purchase #2 $148.72   8.201%   $160.9165   $160.92   $160.90   $160.90  
  Purchase #3 $232.92   3.503%   $241.0792   $241.08   $241.10   $241.10  
  Purchase #4 $89.79   13.649%   $102.0454   $102.05   $102.05   $102.00  
  Purchase #5 $7.26   13.299%   $8.2255   $8.23   $8.25   $8.20  
  Purchase #6 $165.49   3.385%   $171.0918   $171.09   $171.10   $171.10  
  Purchase #7 $95.38   4.150%   $99.3383   $99.34   $99.35   $99.30  
  7 purchase totals = $826.05       $880.8213   $880.83   $880.85   $880.70