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 $73.64   11.854%   $82.3693   $82.37   $82.35   $82.40  
  Purchase #2 $232.96   10.836%   $258.2035   $258.20   $258.20   $258.20  
  Purchase #3 $140.70   12.835%   $158.7588   $158.76   $158.75   $158.80  
  Purchase #4 $235.36   10.504%   $260.0822   $260.08   $260.10   $260.10  
  Purchase #5 $156.55   8.736%   $170.2262   $170.23   $170.25   $170.20  
  Purchase #6 $58.52   10.591%   $64.7179   $64.72   $64.70   $64.70  
  Purchase #7 $19.28   8.534%   $20.9254   $20.93   $20.95   $20.90  
  7 purchase totals = $917.01       $1,015.2833   $1,015.29   $1,015.30   $1,015.30