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 $148.85   6.810%   $158.9867   $158.99   $159.00   $159.00  
  Purchase #2 $203.56   8.271%   $220.3964   $220.40   $220.40   $220.40  
  Purchase #3 $105.56   5.321%   $111.1768   $111.18   $111.20   $111.20  
  Purchase #4 $71.44   13.758%   $81.2687   $81.27   $81.25   $81.30  
  Purchase #5 $118.36   13.759%   $134.6452   $134.65   $134.65   $134.60  
  Purchase #6 $233.46   4.846%   $244.7735   $244.77   $244.75   $244.80  
  Purchase #7 $58.94   7.465%   $63.3399   $63.34   $63.35   $63.30  
  7 purchase totals = $940.17       $1,014.5872   $1,014.60   $1,014.60   $1,014.60