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 $238.76   11.814%   $266.9671   $266.97   $266.95   $267.00  
  Purchase #2 $188.97   11.637%   $210.9604   $210.96   $210.95   $211.00  
  Purchase #3 $89.43   10.488%   $98.8094   $98.81   $98.80   $98.80  
  Purchase #4 $247.25   6.671%   $263.744   $263.74   $263.75   $263.70  
  Purchase #5 $14.80   11.344%   $16.4789   $16.48   $16.50   $16.50  
  Purchase #6 $128.91   5.471%   $135.9627   $135.96   $135.95   $136.00  
  Purchase #7 $241.34   6.730%   $257.5822   $257.58   $257.60   $257.60  
  7 purchase totals = $1,149.46       $1,250.5047   $1,250.50   $1,250.50   $1,250.60