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	$151.53	6.662%	$161.6249	$161.62	$161.60	$161.60
Purchase #2	$23.88	6.865%	$25.5194	$25.52	$25.50	$25.50
Purchase #3	$35.45	13.263%	$40.1517	$40.15	$40.15	$40.20
Purchase #4	$148.34	11.133%	$164.8547	$164.85	$164.85	$164.90
Purchase #5	$80.60	11.624%	$89.9689	$89.97	$89.95	$90.00
Purchase #6	$127.90	11.393%	$142.4716	$142.47	$142.45	$142.50
Purchase #7	$123.82	13.171%	$140.1283	$140.13	$140.15	$140.10
7 purchase totals =	$691.52		$764.7195	$764.71	$764.65	$764.80