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 $59.69   11.718%   $66.6845   $66.68   $66.70   $66.70  
  Purchase #2 $194.33   13.574%   $220.7084   $220.71   $220.70   $220.70  
  Purchase #3 $198.66   8.284%   $215.117   $215.12   $215.10   $215.10  
  Purchase #4 $205.97   10.514%   $227.6257   $227.63   $227.65   $227.60  
  Purchase #5 $131.39   11.536%   $146.5472   $146.55   $146.55   $146.50  
  Purchase #6 $133.98   12.339%   $150.5118   $150.51   $150.50   $150.50  
  Purchase #7 $223.64   7.317%   $240.0037   $240.00   $240.00   $240.00  
  7 purchase totals = $1,147.66       $1,267.1983   $1,267.20   $1,267.20   $1,267.10