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	$7.81	4.332%	$8.1483	$8.15	$8.15	$8.10
Purchase #2	$24.76	13.366%	$28.0694	$28.07	$28.05	$28.10
Purchase #3	$174.34	6.350%	$185.4106	$185.41	$185.40	$185.40
Purchase #4	$55.74	6.690%	$59.469	$59.47	$59.45	$59.50
Purchase #5	$138.58	13.448%	$157.2162	$157.22	$157.20	$157.20
Purchase #6	$139.55	8.627%	$151.589	$151.59	$151.60	$151.60
Purchase #7	$218.72	8.276%	$236.8213	$236.82	$236.80	$236.80
7 purchase totals =	$759.50		$826.7238	$826.73	$826.65	$826.70