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 $91.59   5.224%   $96.3747   $96.37   $96.35   $96.40  
  Purchase #2 $68.93   11.654%   $76.9631   $76.96   $76.95   $77.00  
  Purchase #3 $68.45   8.852%   $74.5092   $74.51   $74.50   $74.50  
  Purchase #4 $244.88   8.496%   $265.685   $265.69   $265.70   $265.70  
  Purchase #5 $160.96   3.692%   $166.9026   $166.90   $166.90   $166.90  
  Purchase #6 $86.77   12.575%   $97.6813   $97.68   $97.70   $97.70  
  Purchase #7 $193.35   8.526%   $209.835   $209.84   $209.85   $209.80  
  7 purchase totals = $914.93       $987.9509   $987.95   $987.95   $988.00