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 $51.70   13.402%   $58.6288   $58.63   $58.65   $58.60  
  Purchase #2 $226.93   9.415%   $248.2955   $248.30   $248.30   $248.30  
  Purchase #3 $112.66   7.252%   $120.8301   $120.83   $120.85   $120.80  
  Purchase #4 $158.54   13.355%   $179.713   $179.71   $179.70   $179.70  
  Purchase #5 $148.71   6.182%   $157.9033   $157.90   $157.90   $157.90  
  Purchase #6 $192.80   11.185%   $214.3647   $214.36   $214.35   $214.40  
  Purchase #7 $57.53   3.873%   $59.7581   $59.76   $59.75   $59.80  
  7 purchase totals = $948.87       $1,039.4935   $1,039.49   $1,039.50   $1,039.50