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 $229.49   13.281%   $259.9686   $259.97   $259.95   $260.00  
  Purchase #2 $204.40   6.568%   $217.825   $217.83   $217.85   $217.80  
  Purchase #3 $240.25   9.461%   $262.9801   $262.98   $263.00   $263.00  
  Purchase #4 $82.80   7.171%   $88.7376   $88.74   $88.75   $88.70  
  Purchase #5 $33.53   10.659%   $37.104   $37.10   $37.10   $37.10  
  Purchase #6 $118.71   3.457%   $122.8138   $122.81   $122.80   $122.80  
  Purchase #7 $64.97   10.570%   $71.8373   $71.84   $71.85   $71.80  
  7 purchase totals = $974.15       $1,061.2664   $1,061.27   $1,061.30   $1,061.20