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 $219.51   13.863%   $249.9407   $249.94   $249.95   $249.90  
  Purchase #2 $124.89   11.190%   $138.8652   $138.87   $138.85   $138.90  
  Purchase #3 $198.84   9.653%   $218.034   $218.03   $218.05   $218.00  
  Purchase #4 $88.36   4.845%   $92.641   $92.64   $92.65   $92.60  
  Purchase #5 $217.39   11.838%   $243.1246   $243.12   $243.10   $243.10  
  Purchase #6 $250.53   10.828%   $277.6574   $277.66   $277.65   $277.70  
  Purchase #7 $50.69   10.599%   $56.0626   $56.06   $56.05   $56.10  
  7 purchase totals = $1,150.21       $1,276.3255   $1,276.32   $1,276.30   $1,276.30