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 $173.78   13.277%   $196.8528   $196.85   $196.85   $196.90  
  Purchase #2 $143.53   3.568%   $148.6512   $148.65   $148.65   $148.70  
  Purchase #3 $186.95   10.787%   $207.1163   $207.12   $207.10   $207.10  
  Purchase #4 $196.48   3.818%   $203.9816   $203.98   $204.00   $204.00  
  Purchase #5 $197.64   6.867%   $211.2119   $211.21   $211.20   $211.20  
  Purchase #6 $222.36   10.402%   $245.4899   $245.49   $245.50   $245.50  
  Purchase #7 $119.37   5.434%   $125.8566   $125.86   $125.85   $125.90  
  7 purchase totals = $1,240.11       $1,339.1603   $1,339.16   $1,339.15   $1,339.30