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 $227.59   7.384%   $244.3952   $244.40   $244.40   $244.40  
  Purchase #2 $22.85   8.106%   $24.7022   $24.70   $24.70   $24.70  
  Purchase #3 $50.51   3.175%   $52.1137   $52.11   $52.10   $52.10  
  Purchase #4 $95.29   10.728%   $105.5127   $105.51   $105.50   $105.50  
  Purchase #5 $172.45   13.557%   $195.829   $195.83   $195.85   $195.80  
  Purchase #6 $149.83   6.290%   $159.2543   $159.25   $159.25   $159.30  
  Purchase #7 $241.61   3.279%   $249.5324   $249.53   $249.55   $249.50  
  7 purchase totals = $960.13       $1,031.3395   $1,031.33   $1,031.35   $1,031.30