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 $230.64   8.531%   $250.3159   $250.32   $250.30   $250.30  
  Purchase #2 $104.48   3.235%   $107.8599   $107.86   $107.85   $107.90  
  Purchase #3 $232.45   3.848%   $241.3947   $241.39   $241.40   $241.40  
  Purchase #4 $53.97   11.208%   $60.019   $60.02   $60.00   $60.00  
  Purchase #5 $161.41   4.394%   $168.5024   $168.50   $168.50   $168.50  
  Purchase #6 $43.63   11.307%   $48.5632   $48.56   $48.55   $48.60  
  Purchase #7 $124.55   10.679%   $137.8507   $137.85   $137.85   $137.90  
  7 purchase totals = $951.13       $1,014.5058   $1,014.50   $1,014.45   $1,014.60