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 $46.94   6.637%   $50.0554   $50.06   $50.05   $50.10  
  Purchase #2 $239.27   9.276%   $261.4647   $261.46   $261.45   $261.50  
  Purchase #3 $76.26   5.677%   $80.5893   $80.59   $80.60   $80.60  
  Purchase #4 $110.31   12.698%   $124.3172   $124.32   $124.30   $124.30  
  Purchase #5 $249.99   10.115%   $275.2765   $275.28   $275.30   $275.30  
  Purchase #6 $193.91   7.601%   $208.6491   $208.65   $208.65   $208.60  
  Purchase #7 $178.77   10.468%   $197.4836   $197.48   $197.50   $197.50  
  7 purchase totals = $1,095.45       $1,197.8358   $1,197.84   $1,197.85   $1,197.90