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 $58.66   12.559%   $66.0271   $66.03   $66.05   $66.00  
  Purchase #2 $96.65   8.591%   $104.9532   $104.95   $104.95   $105.00  
  Purchase #3 $34.92   3.251%   $36.0552   $36.06   $36.05   $36.10  
  Purchase #4 $137.26   3.450%   $141.9955   $142.00   $142.00   $142.00  
  Purchase #5 $210.61   6.262%   $223.7984   $223.80   $223.80   $223.80  
  Purchase #6 $119.58   6.323%   $127.141   $127.14   $127.15   $127.10  
  Purchase #7 $195.97   9.409%   $214.4088   $214.41   $214.40   $214.40  
  7 purchase totals = $853.65       $914.3792   $914.39   $914.40   $914.40