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 $235.49   6.292%   $250.307   $250.31   $250.30   $250.30  
  Purchase #2 $87.52   9.336%   $95.6909   $95.69   $95.70   $95.70  
  Purchase #3 $118.71   12.863%   $133.9797   $133.98   $134.00   $134.00  
  Purchase #4 $68.90   4.452%   $71.9674   $71.97   $71.95   $72.00  
  Purchase #5 $17.40   7.684%   $18.737   $18.74   $18.75   $18.70  
  Purchase #6 $242.35   5.139%   $254.8044   $254.80   $254.80   $254.80  
  Purchase #7 $197.96   8.761%   $215.3033   $215.30   $215.30   $215.30  
  7 purchase totals = $968.33       $1,040.7897   $1,040.79   $1,040.80   $1,040.80