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 $70.97   5.569%   $74.9223   $74.92   $74.90   $74.90  
  Purchase #2 $229.86   11.221%   $255.6526   $255.65   $255.65   $255.70  
  Purchase #3 $192.61   4.691%   $201.6453   $201.65   $201.65   $201.60  
  Purchase #4 $152.39   3.194%   $157.2573   $157.26   $157.25   $157.30  
  Purchase #5 $84.83   11.193%   $94.325   $94.33   $94.35   $94.30  
  Purchase #6 $19.81   11.199%   $22.0285   $22.03   $22.05   $22.00  
  Purchase #7 $95.90   10.450%   $105.9216   $105.92   $105.90   $105.90  
  7 purchase totals = $846.37       $911.7526   $911.76   $911.75   $911.70