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 $57.40   13.269%   $65.0164   $65.02   $65.00   $65.00  
  Purchase #2 $150.52   13.550%   $170.9155   $170.92   $170.90   $170.90  
  Purchase #3 $113.79   5.624%   $120.1895   $120.19   $120.20   $120.20  
  Purchase #4 $86.57   10.515%   $95.6728   $95.67   $95.65   $95.70  
  Purchase #5 $35.65   11.647%   $39.8022   $39.80   $39.80   $39.80  
  Purchase #6 $16.46   4.872%   $17.2619   $17.26   $17.25   $17.30  
  Purchase #7 $242.88   6.658%   $259.051   $259.05   $259.05   $259.10  
  7 purchase totals = $703.27       $767.9093   $767.91   $767.85   $768.00