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 $221.54   12.363%   $248.929   $248.93   $248.95   $248.90  
  Purchase #2 $58.33   9.104%   $63.6404   $63.64   $63.65   $63.60  
  Purchase #3 $95.97   5.417%   $101.1687   $101.17   $101.15   $101.20  
  Purchase #4 $22.31   10.610%   $24.6771   $24.68   $24.70   $24.70  
  Purchase #5 $187.96   3.232%   $194.0349   $194.03   $194.05   $194.00  
  Purchase #6 $179.82   7.121%   $192.625   $192.63   $192.65   $192.60  
  Purchase #7 $163.48   10.868%   $181.247   $181.25   $181.25   $181.20  
  7 purchase totals = $929.41       $1,006.3221   $1,006.33   $1,006.40   $1,006.20