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 $66.94   6.780%   $71.4785   $71.48   $71.50   $71.50  
  Purchase #2 $81.68   5.319%   $86.0246   $86.02   $86.00   $86.00  
  Purchase #3 $83.32   4.429%   $87.0102   $87.01   $87.00   $87.00  
  Purchase #4 $81.91   5.715%   $86.5912   $86.59   $86.60   $86.60  
  Purchase #5 $168.50   3.779%   $174.8676   $174.87   $174.85   $174.90  
  Purchase #6 $81.74   6.325%   $86.9101   $86.91   $86.90   $86.90  
  Purchase #7 $92.75   11.315%   $103.2447   $103.24   $103.25   $103.20  
  7 purchase totals = $656.84       $696.1269   $696.12   $696.10   $696.10