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	$129.56	9.590%	$141.9848	$141.98	$142.00	$142.00
Purchase #2	$172.47	4.606%	$180.414	$180.41	$180.40	$180.40
Purchase #3	$29.71	8.253%	$32.162	$32.16	$32.15	$32.20
Purchase #4	$152.46	8.296%	$165.1081	$165.11	$165.10	$165.10
Purchase #5	$246.30	3.241%	$254.2826	$254.28	$254.30	$254.30
Purchase #6	$104.31	13.595%	$118.4909	$118.49	$118.50	$118.50
Purchase #7	$96.35	8.431%	$104.4733	$104.47	$104.45	$104.50
7 purchase totals =	$931.16		$996.9157	$996.90	$996.90	$997.00