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	$143.73	6.714%	$153.38	$153.38	$153.40	$153.40
Purchase #2	$165.90	13.774%	$188.7511	$188.75	$188.75	$188.80
Purchase #3	$171.54	11.125%	$190.6238	$190.62	$190.60	$190.60
Purchase #4	$146.46	9.870%	$160.9156	$160.92	$160.90	$160.90
Purchase #5	$220.83	8.697%	$240.0356	$240.04	$240.05	$240.00
Purchase #6	$98.51	10.375%	$108.7304	$108.73	$108.75	$108.70
Purchase #7	$31.57	12.796%	$35.6097	$35.61	$35.60	$35.60
7 purchase totals =	$978.54		$1,078.0462	$1,078.05	$1,078.05	$1,078.00