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 $22.83   12.781%   $25.7479   $25.75   $25.75   $25.70  
  Purchase #2 $176.90   5.407%   $186.465   $186.47   $186.45   $186.50  
  Purchase #3 $144.42   10.809%   $160.0304   $160.03   $160.05   $160.00  
  Purchase #4 $98.38   8.547%   $106.7885   $106.79   $106.80   $106.80  
  Purchase #5 $12.67   10.288%   $13.9735   $13.97   $13.95   $14.00  
  Purchase #6 $235.97   4.246%   $245.9893   $245.99   $246.00   $246.00  
  Purchase #7 $211.35   11.746%   $236.1752   $236.18   $236.20   $236.20  
  7 purchase totals = $902.52       $975.1698   $975.18   $975.20   $975.20