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 $59.33   4.729%   $62.1357   $62.14   $62.15   $62.10  
  Purchase #2 $162.67   5.360%   $171.3891   $171.39   $171.40   $171.40  
  Purchase #3 $202.26   12.117%   $226.7678   $226.77   $226.75   $226.80  
  Purchase #4 $159.63   11.781%   $178.436   $178.44   $178.45   $178.40  
  Purchase #5 $107.34   9.609%   $117.6543   $117.65   $117.65   $117.70  
  Purchase #6 $82.65   13.368%   $93.6987   $93.70   $93.70   $93.70  
  Purchase #7 $75.67   6.401%   $80.5136   $80.51   $80.50   $80.50  
  7 purchase totals = $849.55       $930.5952   $930.60   $930.60   $930.60