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 $132.29   11.671%   $147.7296   $147.73   $147.75   $147.70  
  Purchase #2 $97.42   12.221%   $109.3257   $109.33   $109.35   $109.30  
  Purchase #3 $107.30   13.394%   $121.6718   $121.67   $121.65   $121.70  
  Purchase #4 $176.74   4.739%   $185.1157   $185.12   $185.10   $185.10  
  Purchase #5 $44.58   13.145%   $50.44   $50.44   $50.45   $50.40  
  Purchase #6 $163.95   5.232%   $172.5279   $172.53   $172.55   $172.50  
  Purchase #7 $159.72   5.552%   $168.5877   $168.59   $168.60   $168.60  
  7 purchase totals = $882.00       $955.3984   $955.41   $955.45   $955.30