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 $113.29   5.434%   $119.4462   $119.45   $119.45   $119.40  
  Purchase #2 $241.96   3.277%   $249.889   $249.89   $249.90   $249.90  
  Purchase #3 $241.55   6.482%   $257.2073   $257.21   $257.20   $257.20  
  Purchase #4 $152.41   6.516%   $162.341   $162.34   $162.35   $162.30  
  Purchase #5 $63.29   5.694%   $66.8937   $66.89   $66.90   $66.90  
  Purchase #6 $227.48   7.606%   $244.7821   $244.78   $244.80   $244.80  
  Purchase #7 $26.46   13.408%   $30.0078   $30.01   $30.00   $30.00  
  7 purchase totals = $1,066.44       $1,130.5671   $1,130.57   $1,130.60   $1,130.50