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 $226.66   6.406%   $241.1798   $241.18   $241.20   $241.20  
  Purchase #2 $54.74   4.328%   $57.1091   $57.11   $57.10   $57.10  
  Purchase #3 $106.69   11.294%   $118.7396   $118.74   $118.75   $118.70  
  Purchase #4 $201.36   5.245%   $211.9213   $211.92   $211.90   $211.90  
  Purchase #5 $147.83   13.357%   $167.5757   $167.58   $167.60   $167.60  
  Purchase #6 $85.42   4.375%   $89.1571   $89.16   $89.15   $89.20  
  Purchase #7 $14.41   13.240%   $16.3179   $16.32   $16.30   $16.30  
  7 purchase totals = $837.11       $902.0005   $902.01   $902.00   $902.00