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 $46.87   6.657%   $49.9901   $49.99   $50.00   $50.00  
  Purchase #2 $59.43   10.288%   $65.5442   $65.54   $65.55   $65.50  
  Purchase #3 $219.85   3.238%   $226.9687   $226.97   $226.95   $227.00  
  Purchase #4 $228.71   5.202%   $240.6075   $240.61   $240.60   $240.60  
  Purchase #5 $102.79   3.449%   $106.3352   $106.34   $106.35   $106.30  
  Purchase #6 $201.47   7.855%   $217.2955   $217.30   $217.30   $217.30  
  Purchase #7 $98.38   6.868%   $105.1367   $105.14   $105.15   $105.10  
  7 purchase totals = $957.50       $1,011.8779   $1,011.89   $1,011.90   $1,011.80