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 $66.28   11.140%   $73.6636   $73.66   $73.65   $73.70  
  Purchase #2 $231.25   5.859%   $244.7989   $244.80   $244.80   $244.80  
  Purchase #3 $57.81   13.427%   $65.5721   $65.57   $65.55   $65.60  
  Purchase #4 $229.31   9.873%   $251.9498   $251.95   $251.95   $251.90  
  Purchase #5 $201.53   3.869%   $209.3272   $209.33   $209.35   $209.30  
  Purchase #6 $63.54   12.130%   $71.2474   $71.25   $71.25   $71.20  
  Purchase #7 $97.80   6.567%   $104.2225   $104.22   $104.20   $104.20  
  7 purchase totals = $947.52       $1,020.7815   $1,020.78   $1,020.75   $1,020.70