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 $78.53   10.238%   $86.5699   $86.57   $86.55   $86.60  
  Purchase #2 $225.50   8.346%   $244.3202   $244.32   $244.30   $244.30  
  Purchase #3 $125.35   5.832%   $132.6604   $132.66   $132.65   $132.70  
  Purchase #4 $26.56   9.139%   $28.9873   $28.99   $29.00   $29.00  
  Purchase #5 $95.64   12.178%   $107.287   $107.29   $107.30   $107.30  
  Purchase #6 $76.48   9.660%   $83.868   $83.87   $83.85   $83.90  
  Purchase #7 $201.51   8.441%   $218.5195   $218.52   $218.50   $218.50  
  7 purchase totals = $829.57       $902.2123   $902.22   $902.15   $902.30