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 $111.30   13.193%   $125.9838   $125.98   $126.00   $126.00  
  Purchase #2 $39.44   3.582%   $40.8527   $40.85   $40.85   $40.90  
  Purchase #3 $120.37   6.824%   $128.584   $128.58   $128.60   $128.60  
  Purchase #4 $141.33   8.674%   $153.589   $153.59   $153.60   $153.60  
  Purchase #5 $126.97   6.498%   $135.2205   $135.22   $135.20   $135.20  
  Purchase #6 $240.38   12.691%   $270.8866   $270.89   $270.90   $270.90  
  Purchase #7 $186.75   13.236%   $211.4682   $211.47   $211.45   $211.50  
  7 purchase totals = $966.54       $1,066.5848   $1,066.58   $1,066.60   $1,066.70