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 $59.76   8.521%   $64.8521   $64.85   $64.85   $64.90  
  Purchase #2 $195.90   3.446%   $202.6507   $202.65   $202.65   $202.70  
  Purchase #3 $20.54   7.277%   $22.0347   $22.03   $22.05   $22.00  
  Purchase #4 $180.31   13.212%   $204.1326   $204.13   $204.15   $204.10  
  Purchase #5 $42.82   13.822%   $48.7386   $48.74   $48.75   $48.70  
  Purchase #6 $98.37   8.136%   $106.3734   $106.37   $106.35   $106.40  
  Purchase #7 $157.98   12.679%   $178.0103   $178.01   $178.00   $178.00  
  7 purchase totals = $755.68       $826.7924   $826.78   $826.80   $826.80