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 $53.44   10.830%   $59.2276   $59.23   $59.25   $59.20  
  Purchase #2 $232.85   4.786%   $243.9942   $243.99   $244.00   $244.00  
  Purchase #3 $225.75   12.820%   $254.6912   $254.69   $254.70   $254.70  
  Purchase #4 $190.91   12.683%   $215.1231   $215.12   $215.10   $215.10  
  Purchase #5 $127.25   4.759%   $133.3058   $133.31   $133.30   $133.30  
  Purchase #6 $210.47   5.600%   $222.2563   $222.26   $222.25   $222.30  
  Purchase #7 $28.38   6.377%   $30.1898   $30.19   $30.20   $30.20  
  7 purchase totals = $1,069.05       $1,158.7880   $1,158.79   $1,158.80   $1,158.80