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 $206.40   13.776%   $234.8337   $234.83   $234.85   $234.80  
  Purchase #2 $58.93   3.351%   $60.9047   $60.90   $60.90   $60.90  
  Purchase #3 $147.43   7.560%   $158.5757   $158.58   $158.60   $158.60  
  Purchase #4 $125.54   11.702%   $140.2307   $140.23   $140.25   $140.20  
  Purchase #5 $174.83   10.541%   $193.2588   $193.26   $193.25   $193.30  
  Purchase #6 $41.82   11.671%   $46.7008   $46.70   $46.70   $46.70  
  Purchase #7 $210.71   4.319%   $219.8106   $219.81   $219.80   $219.80  
  7 purchase totals = $965.66       $1,054.3150   $1,054.31   $1,054.35   $1,054.30