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 $46.60   3.138%   $48.0623   $48.06   $48.05   $48.10  
  Purchase #2 $249.62   6.184%   $265.0565   $265.06   $265.05   $265.10  
  Purchase #3 $172.73   5.114%   $181.5634   $181.56   $181.55   $181.60  
  Purchase #4 $231.45   13.368%   $262.3902   $262.39   $262.40   $262.40  
  Purchase #5 $162.27   12.375%   $182.3509   $182.35   $182.35   $182.40  
  Purchase #6 $55.30   9.707%   $60.668   $60.67   $60.65   $60.70  
  Purchase #7 $227.43   12.800%   $256.541   $256.54   $256.55   $256.50  
  7 purchase totals = $1,145.40       $1,256.6323   $1,256.63   $1,256.60   $1,256.80