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 $136.75   6.817%   $146.0722   $146.07   $146.05   $146.10  
  Purchase #2 $117.39   6.824%   $125.4007   $125.40   $125.40   $125.40  
  Purchase #3 $239.99   10.740%   $265.7649   $265.76   $265.75   $265.80  
  Purchase #4 $59.93   5.165%   $63.0254   $63.03   $63.05   $63.00  
  Purchase #5 $197.95   5.563%   $208.962   $208.96   $208.95   $209.00  
  Purchase #6 $142.63   7.640%   $153.5269   $153.53   $153.55   $153.50  
  Purchase #7 $52.51   13.523%   $59.6109   $59.61   $59.60   $59.60  
  7 purchase totals = $947.15       $1,022.3630   $1,022.36   $1,022.35   $1,022.40