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 $146.44   5.622%   $154.6729   $154.67   $154.65   $154.70  
  Purchase #2 $64.57   6.387%   $68.6941   $68.69   $68.70   $68.70  
  Purchase #3 $195.25   5.703%   $206.3851   $206.39   $206.40   $206.40  
  Purchase #4 $72.80   10.566%   $80.492   $80.49   $80.50   $80.50  
  Purchase #5 $246.98   5.459%   $260.4626   $260.46   $260.45   $260.50  
  Purchase #6 $214.74   11.808%   $240.0965   $240.10   $240.10   $240.10  
  Purchase #7 $147.88   6.559%   $157.5794   $157.58   $157.60   $157.60  
  7 purchase totals = $1,088.66       $1,168.3826   $1,168.38   $1,168.40   $1,168.50