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 $25.66   13.717%   $29.1798   $29.18   $29.20   $29.20  
  Purchase #2 $40.88   13.518%   $46.4062   $46.41   $46.40   $46.40  
  Purchase #3 $229.97   9.817%   $252.5462   $252.55   $252.55   $252.50  
  Purchase #4 $149.99   11.779%   $167.6573   $167.66   $167.65   $167.70  
  Purchase #5 $77.73   11.174%   $86.4156   $86.42   $86.40   $86.40  
  Purchase #6 $182.90   13.313%   $207.2495   $207.25   $207.25   $207.20  
  Purchase #7 $123.64   11.490%   $137.8462   $137.85   $137.85   $137.80  
  7 purchase totals = $830.77       $927.3008   $927.32   $927.30   $927.20