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 $182.83   10.576%   $202.1661   $202.17   $202.15   $202.20  
  Purchase #2 $206.67   8.543%   $224.3258   $224.33   $224.35   $224.30  
  Purchase #3 $56.63   6.423%   $60.2673   $60.27   $60.25   $60.30  
  Purchase #4 $212.84   5.791%   $225.1656   $225.17   $225.15   $225.20  
  Purchase #5 $231.73   10.676%   $256.4695   $256.47   $256.45   $256.50  
  Purchase #6 $223.76   3.615%   $231.8489   $231.85   $231.85   $231.80  
  Purchase #7 $57.28   10.478%   $63.2818   $63.28   $63.30   $63.30  
  7 purchase totals = $1,171.74       $1,263.5250   $1,263.54   $1,263.50   $1,263.60