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	$29.89	7.256%	$32.0588	$32.06	$32.05	$32.10
Purchase #2	$144.57	8.113%	$156.299	$156.30	$156.30	$156.30
Purchase #3	$244.26	8.152%	$264.1721	$264.17	$264.15	$264.20
Purchase #4	$26.27	4.844%	$27.5425	$27.54	$27.55	$27.50
Purchase #5	$54.48	9.389%	$59.5951	$59.60	$59.60	$59.60
Purchase #6	$202.66	3.314%	$209.3762	$209.38	$209.40	$209.40
Purchase #7	$167.91	13.818%	$191.1118	$191.11	$191.10	$191.10
7 purchase totals =	$870.04		$940.1555	$940.16	$940.15	$940.20