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 $241.25   8.598%   $261.9927   $261.99   $262.00   $262.00  
  Purchase #2 $110.94   6.196%   $117.8138   $117.81   $117.80   $117.80  
  Purchase #3 $42.71   12.215%   $47.927   $47.93   $47.95   $47.90  
  Purchase #4 $182.35   9.695%   $200.0288   $200.03   $200.05   $200.00  
  Purchase #5 $250.49   12.420%   $281.6009   $281.60   $281.60   $281.60  
  Purchase #6 $204.79   4.640%   $214.2923   $214.29   $214.30   $214.30  
  Purchase #7 $219.95   6.643%   $234.5613   $234.56   $234.55   $234.60  
  7 purchase totals = $1,252.48       $1,358.2168   $1,358.21   $1,358.25   $1,358.20