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 $249.41   6.244%   $264.9832   $264.98   $265.00   $265.00  
  Purchase #2 $133.28   4.507%   $139.2869   $139.29   $139.30   $139.30  
  Purchase #3 $141.98   9.286%   $155.1643   $155.16   $155.15   $155.20  
  Purchase #4 $132.64   3.464%   $137.2346   $137.23   $137.25   $137.20  
  Purchase #5 $162.68   9.822%   $178.6584   $178.66   $178.65   $178.70  
  Purchase #6 $138.25   12.142%   $155.0363   $155.04   $155.05   $155.00  
  Purchase #7 $192.45   6.471%   $204.9034   $204.90   $204.90   $204.90  
  7 purchase totals = $1,150.69       $1,235.2671   $1,235.26   $1,235.30   $1,235.30