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 $64.29   6.838%   $68.6862   $68.69   $68.70   $68.70  
  Purchase #2 $110.55   13.613%   $125.5992   $125.60   $125.60   $125.60  
  Purchase #3 $231.73   12.233%   $260.0775   $260.08   $260.10   $260.10  
  Purchase #4 $167.93   5.138%   $176.5582   $176.56   $176.55   $176.60  
  Purchase #5 $10.58   6.259%   $11.2422   $11.24   $11.25   $11.20  
  Purchase #6 $9.63   10.793%   $10.6694   $10.67   $10.65   $10.70  
  Purchase #7 $185.48   7.499%   $199.3891   $199.39   $199.40   $199.40  
  7 purchase totals = $780.19       $852.2218   $852.23   $852.25   $852.30