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	$154.58	11.804%	$172.8266	$172.83	$172.85	$172.80
Purchase #2	$137.76	13.378%	$156.1895	$156.19	$156.20	$156.20
Purchase #3	$193.68	8.758%	$210.6425	$210.64	$210.65	$210.60
Purchase #4	$9.95	4.253%	$10.3732	$10.37	$10.35	$10.40
Purchase #5	$208.29	6.712%	$222.2704	$222.27	$222.25	$222.30
Purchase #6	$73.77	12.817%	$83.2251	$83.23	$83.25	$83.20
Purchase #7	$79.26	9.656%	$86.9133	$86.91	$86.90	$86.90
7 purchase totals =	$857.29		$942.4406	$942.44	$942.45	$942.40