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 $233.91   8.461%   $253.7011   $253.70   $253.70   $253.70  
  Purchase #2 $56.38   10.487%   $62.2926   $62.29   $62.30   $62.30  
  Purchase #3 $211.73   6.317%   $225.105   $225.11   $225.10   $225.10  
  Purchase #4 $92.76   9.858%   $101.9043   $101.90   $101.90   $101.90  
  Purchase #5 $51.65   9.158%   $56.3801   $56.38   $56.40   $56.40  
  Purchase #6 $240.89   6.641%   $256.8875   $256.89   $256.90   $256.90  
  Purchase #7 $232.84   10.467%   $257.2114   $257.21   $257.20   $257.20  
  7 purchase totals = $1,120.16       $1,213.4820   $1,213.48   $1,213.50   $1,213.50