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 $189.76   4.823%   $198.9121   $198.91   $198.90   $198.90  
  Purchase #2 $95.58   6.589%   $101.8778   $101.88   $101.90   $101.90  
  Purchase #3 $166.58   4.564%   $174.1827   $174.18   $174.20   $174.20  
  Purchase #4 $43.76   10.371%   $48.2983   $48.30   $48.30   $48.30  
  Purchase #5 $215.55   12.467%   $242.4226   $242.42   $242.40   $242.40  
  Purchase #6 $208.42   12.589%   $234.658   $234.66   $234.65   $234.70  
  Purchase #7 $39.90   11.533%   $44.5017   $44.50   $44.50   $44.50  
  7 purchase totals = $959.55       $1,044.8532   $1,044.85   $1,044.85   $1,044.90