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	$203.74	9.133%	$222.3476	$222.35	$222.35	$222.30
Purchase #2	$110.89	11.649%	$123.8076	$123.81	$123.80	$123.80
Purchase #3	$15.30	3.201%	$15.7898	$15.79	$15.80	$15.80
Purchase #4	$93.65	7.537%	$100.7084	$100.71	$100.70	$100.70
Purchase #5	$73.69	9.824%	$80.9293	$80.93	$80.95	$80.90
Purchase #6	$223.78	7.613%	$240.8164	$240.82	$240.80	$240.80
Purchase #7	$94.74	8.311%	$102.6138	$102.61	$102.60	$102.60
7 purchase totals =	$815.79		$887.0129	$887.02	$887.00	$886.90