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 $226.68   12.315%   $254.5956   $254.60   $254.60   $254.60  
  Purchase #2 $170.94   3.599%   $177.0921   $177.09   $177.10   $177.10  
  Purchase #3 $243.39   10.328%   $268.5273   $268.53   $268.55   $268.50  
  Purchase #4 $138.78   3.250%   $143.2904   $143.29   $143.30   $143.30  
  Purchase #5 $5.77   4.417%   $6.0249   $6.02   $6.00   $6.00  
  Purchase #6 $118.47   12.323%   $133.0691   $133.07   $133.05   $133.10  
  Purchase #7 $222.72   13.748%   $253.3395   $253.34   $253.35   $253.30  
  7 purchase totals = $1,126.75       $1,235.9389   $1,235.94   $1,235.95   $1,235.90