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 $225.92   10.610%   $249.8901   $249.89   $249.90   $249.90  
  Purchase #2 $125.76   12.331%   $141.2675   $141.27   $141.25   $141.30  
  Purchase #3 $139.60   6.439%   $148.5888   $148.59   $148.60   $148.60  
  Purchase #4 $214.31   7.675%   $230.7583   $230.76   $230.75   $230.80  
  Purchase #5 $94.98   6.603%   $101.2515   $101.25   $101.25   $101.30  
  Purchase #6 $198.86   7.543%   $213.86   $213.86   $213.85   $213.90  
  Purchase #7 $84.33   4.756%   $88.3407   $88.34   $88.35   $88.30  
  7 purchase totals = $1,083.76       $1,173.9569   $1,173.96   $1,173.95   $1,174.10