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 $148.87   10.346%   $164.2721   $164.27   $164.25   $164.30  
  Purchase #2 $97.61   13.501%   $110.7883   $110.79   $110.80   $110.80  
  Purchase #3 $203.86   3.595%   $211.1888   $211.19   $211.20   $211.20  
  Purchase #4 $236.94   4.110%   $246.6782   $246.68   $246.70   $246.70  
  Purchase #5 $41.34   4.169%   $43.0635   $43.06   $43.05   $43.10  
  Purchase #6 $221.60   10.652%   $245.2048   $245.20   $245.20   $245.20  
  Purchase #7 $213.68   5.259%   $224.9174   $224.92   $224.90   $224.90  
  7 purchase totals = $1,163.90       $1,246.1131   $1,246.11   $1,246.10   $1,246.20