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 $191.53   8.593%   $207.9882   $207.99   $208.00   $208.00  
  Purchase #2 $40.28   13.457%   $45.7005   $45.70   $45.70   $45.70  
  Purchase #3 $169.34   12.518%   $190.538   $190.54   $190.55   $190.50  
  Purchase #4 $59.46   9.161%   $64.9071   $64.91   $64.90   $64.90  
  Purchase #5 $232.33   12.621%   $261.6524   $261.65   $261.65   $261.70  
  Purchase #6 $155.75   3.520%   $161.2324   $161.23   $161.25   $161.20  
  Purchase #7 $209.92   7.608%   $225.8907   $225.89   $225.90   $225.90  
  7 purchase totals = $1,058.61       $1,157.9093   $1,157.91   $1,157.95   $1,157.90