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 $57.93   11.494%   $64.5885   $64.59   $64.60   $64.60  
  Purchase #2 $148.53   7.613%   $159.8376   $159.84   $159.85   $159.80  
  Purchase #3 $211.29   9.678%   $231.7386   $231.74   $231.75   $231.70  
  Purchase #4 $200.99   5.255%   $211.552   $211.55   $211.55   $211.60  
  Purchase #5 $180.66   10.203%   $199.0927   $199.09   $199.10   $199.10  
  Purchase #6 $60.64   6.561%   $64.6186   $64.62   $64.60   $64.60  
  Purchase #7 $164.47   8.729%   $178.8266   $178.83   $178.85   $178.80  
  7 purchase totals = $1,024.51       $1,110.2546   $1,110.26   $1,110.30   $1,110.20