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 $50.65   6.227%   $53.804   $53.80   $53.80   $53.80  
  Purchase #2 $85.97   5.497%   $90.6958   $90.70   $90.70   $90.70  
  Purchase #3 $29.55   4.307%   $30.8227   $30.82   $30.80   $30.80  
  Purchase #4 $61.80   3.692%   $64.0817   $64.08   $64.10   $64.10  
  Purchase #5 $160.31   8.742%   $174.3243   $174.32   $174.30   $174.30  
  Purchase #6 $182.28   11.583%   $203.3935   $203.39   $203.40   $203.40  
  Purchase #7 $203.90   6.732%   $217.6265   $217.63   $217.65   $217.60  
  7 purchase totals = $774.46       $834.7485   $834.74   $834.75   $834.70