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 $199.73   13.172%   $226.0384   $226.04   $226.05   $226.00  
  Purchase #2 $119.83   4.455%   $125.1684   $125.17   $125.15   $125.20  
  Purchase #3 $159.70   11.142%   $177.4938   $177.49   $177.50   $177.50  
  Purchase #4 $57.44   11.847%   $64.2449   $64.24   $64.25   $64.20  
  Purchase #5 $55.74   3.629%   $57.7628   $57.76   $57.75   $57.80  
  Purchase #6 $137.46   6.816%   $146.8293   $146.83   $146.85   $146.80  
  Purchase #7 $239.64   13.618%   $272.2742   $272.27   $272.25   $272.30  
  7 purchase totals = $969.54       $1,069.8118   $1,069.80   $1,069.80   $1,069.80