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 $146.57   11.426%   $163.3171   $163.32   $163.30   $163.30  
  Purchase #2 $176.84   10.467%   $195.3498   $195.35   $195.35   $195.30  
  Purchase #3 $38.33   9.610%   $42.0135   $42.01   $42.00   $42.00  
  Purchase #4 $240.48   7.374%   $258.213   $258.21   $258.20   $258.20  
  Purchase #5 $106.33   12.234%   $119.3384   $119.34   $119.35   $119.30  
  Purchase #6 $48.92   3.750%   $50.7545   $50.75   $50.75   $50.80  
  Purchase #7 $162.45   12.870%   $183.3573   $183.36   $183.35   $183.40  
  7 purchase totals = $919.92       $1,012.3436   $1,012.34   $1,012.30   $1,012.30