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 $59.88   10.827%   $66.3632   $66.36   $66.35   $66.40  
  Purchase #2 $28.59   5.639%   $30.2022   $30.20   $30.20   $30.20  
  Purchase #3 $220.43   4.152%   $229.5823   $229.58   $229.60   $229.60  
  Purchase #4 $236.62   3.251%   $244.3125   $244.31   $244.30   $244.30  
  Purchase #5 $221.46   8.110%   $239.4204   $239.42   $239.40   $239.40  
  Purchase #6 $179.79   11.415%   $200.313   $200.31   $200.30   $200.30  
  Purchase #7 $41.57   7.752%   $44.7925   $44.79   $44.80   $44.80  
  7 purchase totals = $988.34       $1,054.9861   $1,054.97   $1,054.95   $1,055.00