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 $90.34   4.330%   $94.2517   $94.25   $94.25   $94.30  
  Purchase #2 $201.99   11.224%   $224.6614   $224.66   $224.65   $224.70  
  Purchase #3 $66.89   13.445%   $75.8834   $75.88   $75.90   $75.90  
  Purchase #4 $241.86   13.772%   $275.169   $275.17   $275.15   $275.20  
  Purchase #5 $179.50   6.791%   $191.6898   $191.69   $191.70   $191.70  
  Purchase #6 $224.69   13.292%   $254.5558   $254.56   $254.55   $254.60  
  Purchase #7 $135.67   3.205%   $140.0182   $140.02   $140.00   $140.00  
  7 purchase totals = $1,140.94       $1,256.2293   $1,256.23   $1,256.20   $1,256.40