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 $56.94   5.717%   $60.1953   $60.20   $60.20   $60.20  
  Purchase #2 $55.80   4.683%   $58.4131   $58.41   $58.40   $58.40  
  Purchase #3 $181.88   12.571%   $204.7441   $204.74   $204.75   $204.70  
  Purchase #4 $212.75   12.104%   $238.5013   $238.50   $238.50   $238.50  
  Purchase #5 $217.57   5.793%   $230.1738   $230.17   $230.15   $230.20  
  Purchase #6 $221.77   12.509%   $249.5112   $249.51   $249.50   $249.50  
  Purchase #7 $46.76   10.415%   $51.6301   $51.63   $51.65   $51.60  
  7 purchase totals = $993.47       $1,093.1689   $1,093.16   $1,093.15   $1,093.10