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 $52.96   12.548%   $59.6054   $59.61   $59.60   $59.60  
  Purchase #2 $167.79   5.369%   $176.7986   $176.80   $176.80   $176.80  
  Purchase #3 $176.34   8.817%   $191.8879   $191.89   $191.90   $191.90  
  Purchase #4 $186.60   3.665%   $193.4389   $193.44   $193.45   $193.40  
  Purchase #5 $73.69   11.840%   $82.4149   $82.41   $82.40   $82.40  
  Purchase #6 $73.35   9.857%   $80.5801   $80.58   $80.60   $80.60  
  Purchase #7 $107.92   8.133%   $116.6971   $116.70   $116.70   $116.70  
  7 purchase totals = $838.65       $901.4229   $901.43   $901.45   $901.40