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 $78.67   10.554%   $86.9728   $86.97   $86.95   $87.00  
  Purchase #2 $175.58   7.449%   $188.659   $188.66   $188.65   $188.70  
  Purchase #3 $93.97   7.233%   $100.7669   $100.77   $100.75   $100.80  
  Purchase #4 $153.94   8.858%   $167.576   $167.58   $167.60   $167.60  
  Purchase #5 $90.98   8.433%   $98.6523   $98.65   $98.65   $98.70  
  Purchase #6 $67.69   5.174%   $71.1923   $71.19   $71.20   $71.20  
  Purchase #7 $17.47   8.230%   $18.9078   $18.91   $18.90   $18.90  
  7 purchase totals = $678.30       $732.7271   $732.73   $732.70   $732.90