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 $197.26   13.401%   $223.6948   $223.69   $223.70   $223.70  
  Purchase #2 $158.42   4.604%   $165.7137   $165.71   $165.70   $165.70  
  Purchase #3 $159.79   11.213%   $177.7073   $177.71   $177.70   $177.70  
  Purchase #4 $15.48   8.157%   $16.7427   $16.74   $16.75   $16.70  
  Purchase #5 $5.79   10.387%   $6.3914   $6.39   $6.40   $6.40  
  Purchase #6 $202.79   11.594%   $226.3015   $226.30   $226.30   $226.30  
  Purchase #7 $191.42   4.181%   $199.4233   $199.42   $199.40   $199.40  
  7 purchase totals = $930.95       $1,015.9747   $1,015.96   $1,015.95   $1,015.90