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 $76.26   11.557%   $85.0734   $85.07   $85.05   $85.10  
  Purchase #2 $118.71   7.284%   $127.3568   $127.36   $127.35   $127.40  
  Purchase #3 $65.56   5.140%   $68.9298   $68.93   $68.95   $68.90  
  Purchase #4 $193.86   5.516%   $204.5533   $204.55   $204.55   $204.60  
  Purchase #5 $31.56   7.823%   $34.0289   $34.03   $34.05   $34.00  
  Purchase #6 $142.29   12.555%   $160.1545   $160.15   $160.15   $160.20  
  Purchase #7 $183.90   12.788%   $207.4171   $207.42   $207.40   $207.40  
  7 purchase totals = $812.14       $887.5138   $887.51   $887.50   $887.60