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 $79.97   8.171%   $86.5043   $86.50   $86.50   $86.50  
  Purchase #2 $144.53   12.753%   $162.9619   $162.96   $162.95   $163.00  
  Purchase #3 $51.44   8.426%   $55.7743   $55.77   $55.75   $55.80  
  Purchase #4 $151.55   6.558%   $161.4886   $161.49   $161.50   $161.50  
  Purchase #5 $203.88   13.672%   $231.7545   $231.75   $231.75   $231.80  
  Purchase #6 $22.45   13.697%   $25.525   $25.53   $25.55   $25.50  
  Purchase #7 $123.49   12.550%   $138.988   $138.99   $139.00   $139.00  
  7 purchase totals = $777.31       $862.9966   $862.99   $863.00   $863.10