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 $30.33   7.567%   $32.6251   $32.63   $32.65   $32.60  
  Purchase #2 $84.76   10.152%   $93.3648   $93.36   $93.35   $93.40  
  Purchase #3 $240.76   6.397%   $256.1614   $256.16   $256.15   $256.20  
  Purchase #4 $220.43   9.667%   $241.739   $241.74   $241.75   $241.70  
  Purchase #5 $189.74   9.773%   $208.2833   $208.28   $208.30   $208.30  
  Purchase #6 $238.53   12.700%   $268.8233   $268.82   $268.80   $268.80  
  Purchase #7 $81.71   10.119%   $89.9782   $89.98   $90.00   $90.00  
  7 purchase totals = $1,086.26       $1,190.9751   $1,190.97   $1,191.00   $1,191.00