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 $149.47   12.234%   $167.7562   $167.76   $167.75   $167.80  
  Purchase #2 $231.92   4.827%   $243.1148   $243.11   $243.10   $243.10  
  Purchase #3 $200.77   7.569%   $215.9663   $215.97   $215.95   $216.00  
  Purchase #4 $244.49   3.745%   $253.6462   $253.65   $253.65   $253.60  
  Purchase #5 $162.27   4.507%   $169.5835   $169.58   $169.60   $169.60  
  Purchase #6 $172.89   11.232%   $192.309   $192.31   $192.30   $192.30  
  Purchase #7 $227.42   10.198%   $250.6123   $250.61   $250.60   $250.60  
  7 purchase totals = $1,389.23       $1,492.9883   $1,492.99   $1,492.95   $1,493.00