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 $227.62   8.790%   $247.6278   $247.63   $247.65   $247.60  
  Purchase #2 $206.91   11.269%   $230.2267   $230.23   $230.25   $230.20  
  Purchase #3 $127.74   4.356%   $133.3044   $133.30   $133.30   $133.30  
  Purchase #4 $213.33   6.779%   $227.7916   $227.79   $227.80   $227.80  
  Purchase #5 $51.49   6.857%   $55.0207   $55.02   $55.00   $55.00  
  Purchase #6 $76.44   5.429%   $80.5899   $80.59   $80.60   $80.60  
  Purchase #7 $209.39   7.199%   $224.464   $224.46   $224.45   $224.50  
  7 purchase totals = $1,112.92       $1,199.0251   $1,199.02   $1,199.05   $1,199.00