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 $188.95   7.561%   $203.2365   $203.24   $203.25   $203.20  
  Purchase #2 $79.97   12.833%   $90.2326   $90.23   $90.25   $90.20  
  Purchase #3 $154.30   12.419%   $173.4625   $173.46   $173.45   $173.50  
  Purchase #4 $87.66   4.744%   $91.8186   $91.82   $91.80   $91.80  
  Purchase #5 $222.83   11.759%   $249.0326   $249.03   $249.05   $249.00  
  Purchase #6 $201.84   4.315%   $210.5494   $210.55   $210.55   $210.50  
  Purchase #7 $169.72   3.766%   $176.1117   $176.11   $176.10   $176.10  
  7 purchase totals = $1,105.27       $1,194.4439   $1,194.44   $1,194.45   $1,194.30