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 $58.29   7.839%   $62.8594   $62.86   $62.85   $62.90  
  Purchase #2 $189.84   13.136%   $214.7774   $214.78   $214.80   $214.80  
  Purchase #3 $186.69   13.400%   $211.7065   $211.71   $211.70   $211.70  
  Purchase #4 $87.29   11.349%   $97.1965   $97.20   $97.20   $97.20  
  Purchase #5 $192.46   11.397%   $214.3947   $214.39   $214.40   $214.40  
  Purchase #6 $90.87   3.720%   $94.2504   $94.25   $94.25   $94.30  
  Purchase #7 $233.34   3.554%   $241.6329   $241.63   $241.65   $241.60  
  7 purchase totals = $1,038.78       $1,136.8178   $1,136.82   $1,136.85   $1,136.90