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 $243.78   8.516%   $264.5403   $264.54   $264.55   $264.50  
  Purchase #2 $61.82   10.439%   $68.2734   $68.27   $68.25   $68.30  
  Purchase #3 $33.90   8.688%   $36.8452   $36.85   $36.85   $36.80  
  Purchase #4 $68.40   4.327%   $71.3597   $71.36   $71.35   $71.40  
  Purchase #5 $71.57   6.127%   $75.9551   $75.96   $75.95   $76.00  
  Purchase #6 $57.36   7.733%   $61.7956   $61.80   $61.80   $61.80  
  Purchase #7 $35.73   10.520%   $39.4888   $39.49   $39.50   $39.50  
  7 purchase totals = $572.56       $618.2581   $618.27   $618.25   $618.30