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 $147.83   10.456%   $163.2871   $163.29   $163.30   $163.30  
  Purchase #2 $178.89   9.381%   $195.6717   $195.67   $195.65   $195.70  
  Purchase #3 $244.87   9.400%   $267.8878   $267.89   $267.90   $267.90  
  Purchase #4 $169.69   9.592%   $185.9667   $185.97   $185.95   $186.00  
  Purchase #5 $132.73   11.255%   $147.6688   $147.67   $147.65   $147.70  
  Purchase #6 $201.75   3.717%   $209.249   $209.25   $209.25   $209.20  
  Purchase #7 $18.30   12.451%   $20.5785   $20.58   $20.60   $20.60  
  7 purchase totals = $1,094.06       $1,190.3096   $1,190.32   $1,190.30   $1,190.40