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 $175.77   8.669%   $191.0075   $191.01   $191.00   $191.00  
  Purchase #2 $40.89   13.486%   $46.4044   $46.40   $46.40   $46.40  
  Purchase #3 $165.36   7.163%   $177.2047   $177.20   $177.20   $177.20  
  Purchase #4 $70.37   6.562%   $74.9877   $74.99   $75.00   $75.00  
  Purchase #5 $161.75   3.350%   $167.1686   $167.17   $167.15   $167.20  
  Purchase #6 $239.39   11.861%   $267.784   $267.78   $267.80   $267.80  
  Purchase #7 $51.97   12.381%   $58.4044   $58.40   $58.40   $58.40  
  7 purchase totals = $905.50       $982.9613   $982.95   $982.95   $983.00