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 $243.49   4.219%   $253.7628   $253.76   $253.75   $253.80  
  Purchase #2 $64.95   10.502%   $71.771   $71.77   $71.75   $71.80  
  Purchase #3 $39.80   12.278%   $44.6866   $44.69   $44.70   $44.70  
  Purchase #4 $80.67   6.557%   $85.9595   $85.96   $85.95   $86.00  
  Purchase #5 $123.70   6.842%   $132.1636   $132.16   $132.15   $132.20  
  Purchase #6 $22.50   11.165%   $25.0121   $25.01   $25.00   $25.00  
  Purchase #7 $18.48   4.397%   $19.2926   $19.29   $19.30   $19.30  
  7 purchase totals = $593.59       $632.6482   $632.64   $632.60   $632.80