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	$84.32	7.478%	$90.6254	$90.63	$90.65	$90.60
Purchase #2	$75.93	9.449%	$83.1046	$83.10	$83.10	$83.10
Purchase #3	$228.54	7.109%	$244.7869	$244.79	$244.80	$244.80
Purchase #4	$97.26	5.230%	$102.3467	$102.35	$102.35	$102.30
Purchase #5	$155.57	7.425%	$167.1211	$167.12	$167.10	$167.10
Purchase #6	$180.79	10.568%	$199.8959	$199.90	$199.90	$199.90
Purchase #7	$195.52	13.318%	$221.5594	$221.56	$221.55	$221.60
7 purchase totals =	$1,017.93		$1,109.4400	$1,109.45	$1,109.45	$1,109.40