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 $60.46   10.282%   $66.6765   $66.68   $66.70   $66.70  
  Purchase #2 $202.73   8.654%   $220.2743   $220.27   $220.25   $220.30  
  Purchase #3 $204.71   10.769%   $226.7552   $226.76   $226.75   $226.80  
  Purchase #4 $76.80   8.827%   $83.5791   $83.58   $83.60   $83.60  
  Purchase #5 $212.33   8.234%   $229.8133   $229.81   $229.80   $229.80  
  Purchase #6 $115.82   12.203%   $129.9535   $129.95   $129.95   $130.00  
  Purchase #7 $216.66   12.596%   $243.9505   $243.95   $243.95   $244.00  
  7 purchase totals = $1,089.51       $1,201.0024   $1,201.00   $1,201.00   $1,201.20