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 $72.93   3.482%   $75.4694   $75.47   $75.45   $75.50  
  Purchase #2 $73.34   9.838%   $80.5552   $80.56   $80.55   $80.60  
  Purchase #3 $239.76   13.694%   $272.5927   $272.59   $272.60   $272.60  
  Purchase #4 $238.68   13.233%   $270.2645   $270.26   $270.25   $270.30  
  Purchase #5 $214.50   4.212%   $223.5347   $223.53   $223.55   $223.50  
  Purchase #6 $125.81   3.269%   $129.9227   $129.92   $129.90   $129.90  
  Purchase #7 $59.81   8.445%   $64.861   $64.86   $64.85   $64.90  
  7 purchase totals = $1,024.83       $1,117.2002   $1,117.19   $1,117.15   $1,117.30