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	$73.78	6.125%	$78.299	$78.30	$78.30	$78.30
Purchase #2	$134.72	12.111%	$151.0359	$151.04	$151.05	$151.00
Purchase #3	$83.46	9.288%	$91.2118	$91.21	$91.20	$91.20
Purchase #4	$29.38	5.715%	$31.0591	$31.06	$31.05	$31.10
Purchase #5	$51.36	9.369%	$56.1719	$56.17	$56.15	$56.20
Purchase #6	$39.43	10.361%	$43.5153	$43.52	$43.50	$43.50
Purchase #7	$36.61	11.324%	$40.7557	$40.76	$40.75	$40.80
7 purchase totals =	$448.74		$492.0487	$492.06	$492.00	$492.10