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 $87.99   7.782%   $94.8374   $94.84   $94.85   $94.80  
  Purchase #2 $32.76   9.178%   $35.7667   $35.77   $35.75   $35.80  
  Purchase #3 $191.38   12.232%   $214.7896   $214.79   $214.80   $214.80  
  Purchase #4 $213.48   9.477%   $233.7115   $233.71   $233.70   $233.70  
  Purchase #5 $68.98   5.752%   $72.9477   $72.95   $72.95   $72.90  
  Purchase #6 $188.49   7.308%   $202.2648   $202.26   $202.25   $202.30  
  Purchase #7 $142.68   12.833%   $160.9901   $160.99   $161.00   $161.00  
  7 purchase totals = $925.76       $1,015.3078   $1,015.31   $1,015.30   $1,015.30