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 $96.62   7.678%   $104.0385   $104.04   $104.05   $104.00  
  Purchase #2 $224.68   8.833%   $244.526   $244.53   $244.55   $244.50  
  Purchase #3 $72.74   10.145%   $80.1195   $80.12   $80.10   $80.10  
  Purchase #4 $62.83   11.442%   $70.019   $70.02   $70.00   $70.00  
  Purchase #5 $61.60   3.510%   $63.7622   $63.76   $63.75   $63.80  
  Purchase #6 $215.91   11.457%   $240.6468   $240.65   $240.65   $240.60  
  Purchase #7 $197.39   11.128%   $219.3556   $219.36   $219.35   $219.40  
  7 purchase totals = $931.77       $1,022.4676   $1,022.48   $1,022.45   $1,022.40