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 $119.67   12.826%   $135.0189   $135.02   $135.00   $135.00  
  Purchase #2 $57.67   4.829%   $60.4549   $60.45   $60.45   $60.50  
  Purchase #3 $147.66   10.785%   $163.5851   $163.59   $163.60   $163.60  
  Purchase #4 $13.93   6.680%   $14.8605   $14.86   $14.85   $14.90  
  Purchase #5 $48.77   10.564%   $53.9221   $53.92   $53.90   $53.90  
  Purchase #6 $175.63   5.185%   $184.7364   $184.74   $184.75   $184.70  
  Purchase #7 $176.33   13.409%   $199.9741   $199.97   $199.95   $200.00  
  7 purchase totals = $739.66       $812.5520   $812.55   $812.50   $812.60