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 $78.48   10.659%   $86.8452   $86.85   $86.85   $86.80  
  Purchase #2 $223.32   9.518%   $244.5756   $244.58   $244.60   $244.60  
  Purchase #3 $58.79   13.303%   $66.6108   $66.61   $66.60   $66.60  
  Purchase #4 $222.99   13.550%   $253.2051   $253.21   $253.20   $253.20  
  Purchase #5 $9.85   9.417%   $10.7776   $10.78   $10.80   $10.80  
  Purchase #6 $248.91   11.765%   $278.1943   $278.19   $278.20   $278.20  
  Purchase #7 $76.62   8.289%   $82.971   $82.97   $82.95   $83.00  
  7 purchase totals = $918.96       $1,023.1796   $1,023.19   $1,023.20   $1,023.20