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	$55.25	12.472%	$62.1408	$62.14	$62.15	$62.10
Purchase #2	$151.72	12.147%	$170.1494	$170.15	$170.15	$170.10
Purchase #3	$177.38	11.800%	$198.3108	$198.31	$198.30	$198.30
Purchase #4	$148.56	12.594%	$167.2696	$167.27	$167.25	$167.30
Purchase #5	$36.36	6.309%	$38.654	$38.65	$38.65	$38.70
Purchase #6	$187.33	6.861%	$200.1827	$200.18	$200.20	$200.20
Purchase #7	$78.31	8.624%	$85.0635	$85.06	$85.05	$85.10
7 purchase totals =	$834.91		$921.7708	$921.76	$921.75	$921.80