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	$225.29	11.361%	$250.8852	$250.89	$250.90	$250.90
Purchase #2	$35.42	8.109%	$38.2922	$38.29	$38.30	$38.30
Purchase #3	$147.57	7.136%	$158.1006	$158.10	$158.10	$158.10
Purchase #4	$140.80	8.347%	$152.5526	$152.55	$152.55	$152.60
Purchase #5	$72.87	6.696%	$77.7494	$77.75	$77.75	$77.70
Purchase #6	$97.93	6.511%	$104.3062	$104.31	$104.30	$104.30
Purchase #7	$99.59	4.807%	$104.3773	$104.38	$104.40	$104.40
7 purchase totals =	$819.47		$886.2635	$886.27	$886.30	$886.30