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 $68.55   8.717%   $74.5255   $74.53   $74.55   $74.50  
  Purchase #2 $114.95   3.597%   $119.0848   $119.08   $119.10   $119.10  
  Purchase #3 $226.30   12.702%   $255.0446   $255.04   $255.05   $255.00  
  Purchase #4 $240.99   9.151%   $263.043   $263.04   $263.05   $263.00  
  Purchase #5 $111.42   8.653%   $121.0612   $121.06   $121.05   $121.10  
  Purchase #6 $221.37   5.710%   $234.0102   $234.01   $234.00   $234.00  
  Purchase #7 $236.87   10.468%   $261.6656   $261.67   $261.65   $261.70  
  7 purchase totals = $1,220.45       $1,328.4349   $1,328.43   $1,328.45   $1,328.40