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	$180.69	5.137%	$189.972	$189.97	$189.95	$190.00
Purchase #2	$91.30	8.462%	$99.0258	$99.03	$99.05	$99.00
Purchase #3	$237.67	7.404%	$255.2671	$255.27	$255.25	$255.30
Purchase #4	$55.98	9.828%	$61.4817	$61.48	$61.50	$61.50
Purchase #5	$146.83	3.570%	$152.0718	$152.07	$152.05	$152.10
Purchase #6	$20.83	11.253%	$23.174	$23.17	$23.15	$23.20
Purchase #7	$113.79	4.693%	$119.1302	$119.13	$119.15	$119.10
7 purchase totals =	$847.09		$900.1226	$900.12	$900.10	$900.20