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 $58.57   13.295%   $66.3569   $66.36   $66.35   $66.40  
  Purchase #2 $162.75   8.766%   $177.0167   $177.02   $177.00   $177.00  
  Purchase #3 $82.55   8.210%   $89.3274   $89.33   $89.35   $89.30  
  Purchase #4 $76.98   13.872%   $87.6587   $87.66   $87.65   $87.70  
  Purchase #5 $82.27   3.311%   $84.994   $84.99   $85.00   $85.00  
  Purchase #6 $107.86   13.412%   $122.3262   $122.33   $122.35   $122.30  
  Purchase #7 $160.32   10.711%   $177.4919   $177.49   $177.50   $177.50  
  7 purchase totals = $731.30       $805.1718   $805.18   $805.20   $805.20