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 $224.37   10.555%   $248.0523   $248.05   $248.05   $248.10  
  Purchase #2 $175.88   3.306%   $181.6946   $181.69   $181.70   $181.70  
  Purchase #3 $61.73   12.125%   $69.2148   $69.21   $69.20   $69.20  
  Purchase #4 $246.43   4.430%   $257.3468   $257.35   $257.35   $257.30  
  Purchase #5 $122.78   6.324%   $130.5446   $130.54   $130.55   $130.50  
  Purchase #6 $39.51   4.833%   $41.4195   $41.42   $41.40   $41.40  
  Purchase #7 $36.52   11.617%   $40.7625   $40.76   $40.75   $40.80  
  7 purchase totals = $907.22       $969.0351   $969.02   $969.00   $969.00