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 $87.59   8.752%   $95.2559   $95.26   $95.25   $95.30  
  Purchase #2 $216.42   11.138%   $240.5249   $240.52   $240.50   $240.50  
  Purchase #3 $27.37   10.395%   $30.2151   $30.22   $30.20   $30.20  
  Purchase #4 $155.43   13.837%   $176.9368   $176.94   $176.95   $176.90  
  Purchase #5 $185.95   4.270%   $193.8901   $193.89   $193.90   $193.90  
  Purchase #6 $37.87   3.608%   $39.2363   $39.24   $39.25   $39.20  
  Purchase #7 $127.81   10.384%   $141.0818   $141.08   $141.10   $141.10  
  7 purchase totals = $838.44       $917.1409   $917.15   $917.15   $917.10