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 $23.56   13.251%   $26.6819   $26.68   $26.70   $26.70  
  Purchase #2 $192.42   6.355%   $204.6483   $204.65   $204.65   $204.60  
  Purchase #3 $155.71   8.157%   $168.4113   $168.41   $168.40   $168.40  
  Purchase #4 $153.41   10.810%   $169.9936   $169.99   $170.00   $170.00  
  Purchase #5 $245.68   5.377%   $258.8902   $258.89   $258.90   $258.90  
  Purchase #6 $224.87   9.655%   $246.5812   $246.58   $246.60   $246.60  
  Purchase #7 $200.66   5.265%   $211.2247   $211.22   $211.20   $211.20  
  7 purchase totals = $1,196.31       $1,286.4312   $1,286.42   $1,286.45   $1,286.40