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 $175.30   4.619%   $183.3971   $183.40   $183.40   $183.40  
  Purchase #2 $51.87   13.540%   $58.8932   $58.89   $58.90   $58.90  
  Purchase #3 $207.96   4.673%   $217.678   $217.68   $217.70   $217.70  
  Purchase #4 $98.40   9.201%   $107.4538   $107.45   $107.45   $107.50  
  Purchase #5 $218.37   5.332%   $230.0135   $230.01   $230.00   $230.00  
  Purchase #6 $206.96   7.314%   $222.0971   $222.10   $222.10   $222.10  
  Purchase #7 $183.69   12.781%   $207.1674   $207.17   $207.15   $207.20  
  7 purchase totals = $1,142.55       $1,226.7001   $1,226.70   $1,226.70   $1,226.80