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 $59.82   10.263%   $65.9593   $65.96   $65.95   $66.00  
  Purchase #2 $113.36   5.828%   $119.9666   $119.97   $119.95   $120.00  
  Purchase #3 $75.37   11.593%   $84.1076   $84.11   $84.10   $84.10  
  Purchase #4 $239.72   11.206%   $266.583   $266.58   $266.60   $266.60  
  Purchase #5 $166.74   6.544%   $177.6515   $177.65   $177.65   $177.70  
  Purchase #6 $42.83   12.339%   $48.1148   $48.11   $48.10   $48.10  
  Purchase #7 $37.80   13.524%   $42.9121   $42.91   $42.90   $42.90  
  7 purchase totals = $735.64       $805.2949   $805.29   $805.25   $805.40