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 $87.61   9.427%   $95.869   $95.87   $95.85   $95.90  
  Purchase #2 $27.34   8.191%   $29.5794   $29.58   $29.60   $29.60  
  Purchase #3 $228.81   7.620%   $246.2453   $246.25   $246.25   $246.20  
  Purchase #4 $66.46   6.121%   $70.528   $70.53   $70.55   $70.50  
  Purchase #5 $143.25   12.674%   $161.4055   $161.41   $161.40   $161.40  
  Purchase #6 $229.47   6.741%   $244.9386   $244.94   $244.95   $244.90  
  Purchase #7 $130.68   3.201%   $134.8631   $134.86   $134.85   $134.90  
  7 purchase totals = $913.62       $983.4289   $983.44   $983.45   $983.40