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	$240.76	12.330%	$270.4457	$270.45	$270.45	$270.40
Purchase #2	$46.95	13.569%	$53.3206	$53.32	$53.30	$53.30
Purchase #3	$23.78	5.392%	$25.0622	$25.06	$25.05	$25.10
Purchase #4	$37.29	3.802%	$38.7078	$38.71	$38.70	$38.70
Purchase #5	$35.27	12.869%	$39.8089	$39.81	$39.80	$39.80
Purchase #6	$104.89	12.823%	$118.34	$118.34	$118.35	$118.30
Purchase #7	$244.53	12.614%	$275.375	$275.38	$275.40	$275.40
7 purchase totals =	$733.47		$821.0602	$821.07	$821.05	$821.00