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 $188.62   6.863%   $201.565   $201.57   $201.55   $201.60  
  Purchase #2 $244.49   6.634%   $260.7095   $260.71   $260.70   $260.70  
  Purchase #3 $28.44   11.835%   $31.8059   $31.81   $31.80   $31.80  
  Purchase #4 $25.58   11.401%   $28.4964   $28.50   $28.50   $28.50  
  Purchase #5 $106.34   6.427%   $113.1745   $113.17   $113.15   $113.20  
  Purchase #6 $231.58   10.557%   $256.0279   $256.03   $256.05   $256.00  
  Purchase #7 $21.34   9.164%   $23.2956   $23.30   $23.30   $23.30  
  7 purchase totals = $846.39       $915.0748   $915.09   $915.05   $915.10