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 $77.87   11.657%   $86.9473   $86.95   $86.95   $86.90  
  Purchase #2 $164.77   10.374%   $181.8632   $181.86   $181.85   $181.90  
  Purchase #3 $103.52   12.627%   $116.5915   $116.59   $116.60   $116.60  
  Purchase #4 $168.71   5.784%   $178.4682   $178.47   $178.45   $178.50  
  Purchase #5 $87.60   7.568%   $94.2296   $94.23   $94.25   $94.20  
  Purchase #6 $122.88   13.631%   $139.6298   $139.63   $139.65   $139.60  
  Purchase #7 $46.84   6.538%   $49.9024   $49.90   $49.90   $49.90  
  7 purchase totals = $772.19       $847.6320   $847.63   $847.65   $847.60