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 $241.62   6.353%   $256.9701   $256.97   $256.95   $257.00  
  Purchase #2 $156.74   8.562%   $170.1601   $170.16   $170.15   $170.20  
  Purchase #3 $244.51   11.453%   $272.5137   $272.51   $272.50   $272.50  
  Purchase #4 $181.76   6.746%   $194.0215   $194.02   $194.00   $194.00  
  Purchase #5 $32.32   9.273%   $35.317   $35.32   $35.30   $35.30  
  Purchase #6 $241.60   3.840%   $250.8774   $250.88   $250.90   $250.90  
  Purchase #7 $133.91   13.642%   $152.178   $152.18   $152.20   $152.20  
  7 purchase totals = $1,232.46       $1,332.0378   $1,332.04   $1,332.00   $1,332.10