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	$35.27	5.109%	$37.0719	$37.07	$37.05	$37.10
Purchase #2	$81.76	6.199%	$86.8283	$86.83	$86.85	$86.80
Purchase #3	$77.72	6.124%	$82.4796	$82.48	$82.50	$82.50
Purchase #4	$30.35	7.543%	$32.6393	$32.64	$32.65	$32.60
Purchase #5	$180.31	7.198%	$193.2887	$193.29	$193.30	$193.30
Purchase #6	$73.59	9.556%	$80.6223	$80.62	$80.60	$80.60
Purchase #7	$54.75	9.160%	$59.7651	$59.77	$59.75	$59.80
7 purchase totals =	$533.75		$572.6952	$572.70	$572.70	$572.70