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	$32.40	9.709%	$35.5457	$35.55	$35.55	$35.50
Purchase #2	$221.89	12.723%	$250.1211	$250.12	$250.10	$250.10
Purchase #3	$104.65	10.749%	$115.8988	$115.90	$115.90	$115.90
Purchase #4	$143.32	11.585%	$159.9236	$159.92	$159.90	$159.90
Purchase #5	$33.55	11.324%	$37.3492	$37.35	$37.35	$37.30
Purchase #6	$88.54	11.833%	$99.0169	$99.02	$99.00	$99.00
Purchase #7	$224.97	8.728%	$244.6054	$244.61	$244.60	$244.60
7 purchase totals =	$849.32		$942.4607	$942.47	$942.40	$942.30