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	$39.51	7.362%	$42.4187	$42.42	$42.40	$42.40
Purchase #2	$235.80	5.870%	$249.6415	$249.64	$249.65	$249.60
Purchase #3	$167.59	8.385%	$181.6424	$181.64	$181.65	$181.60
Purchase #4	$98.89	13.613%	$112.3519	$112.35	$112.35	$112.40
Purchase #5	$181.78	5.335%	$191.478	$191.48	$191.50	$191.50
Purchase #6	$78.86	12.544%	$88.7522	$88.75	$88.75	$88.80
Purchase #7	$200.58	12.127%	$224.9043	$224.90	$224.90	$224.90
7 purchase totals =	$1,003.01		$1,091.1890	$1,091.18	$1,091.20	$1,091.20