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 $60.33   3.767%   $62.6026   $62.60   $62.60   $62.60  
  Purchase #2 $228.59   8.123%   $247.1584   $247.16   $247.15   $247.20  
  Purchase #3 $87.34   7.778%   $94.1333   $94.13   $94.15   $94.10  
  Purchase #4 $61.89   11.158%   $68.7957   $68.80   $68.80   $68.80  
  Purchase #5 $86.38   9.629%   $94.6975   $94.70   $94.70   $94.70  
  Purchase #6 $177.53   13.219%   $200.9977   $201.00   $201.00   $201.00  
  Purchase #7 $36.86   6.521%   $39.2636   $39.26   $39.25   $39.30  
  7 purchase totals = $738.92       $807.6488   $807.65   $807.65   $807.70