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 $242.29   10.745%   $268.3241   $268.32   $268.30   $268.30  
  Purchase #2 $63.30   8.269%   $68.5343   $68.53   $68.55   $68.50  
  Purchase #3 $242.93   6.132%   $257.8265   $257.83   $257.85   $257.80  
  Purchase #4 $51.69   5.422%   $54.4926   $54.49   $54.50   $54.50  
  Purchase #5 $233.79   11.356%   $260.3392   $260.34   $260.35   $260.30  
  Purchase #6 $200.70   12.456%   $225.6992   $225.70   $225.70   $225.70  
  Purchase #7 $177.47   9.646%   $194.5888   $194.59   $194.60   $194.60  
  7 purchase totals = $1,212.17       $1,329.8047   $1,329.80   $1,329.85   $1,329.70