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 $32.89   6.413%   $34.9992   $35.00   $35.00   $35.00  
  Purchase #2 $121.45   12.607%   $136.7612   $136.76   $136.75   $136.80  
  Purchase #3 $151.46   7.126%   $162.253   $162.25   $162.25   $162.30  
  Purchase #4 $227.85   9.565%   $249.6439   $249.64   $249.65   $249.60  
  Purchase #5 $247.62   11.404%   $275.8586   $275.86   $275.85   $275.90  
  Purchase #6 $120.31   4.135%   $125.2848   $125.28   $125.30   $125.30  
  Purchase #7 $123.45   13.572%   $140.2046   $140.20   $140.20   $140.20  
  7 purchase totals = $1,025.03       $1,125.0053   $1,124.99   $1,125.00   $1,125.10