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	$125.42	3.510%	$129.8222	$129.82	$129.80	$129.80
Purchase #2	$33.85	10.129%	$37.2787	$37.28	$37.30	$37.30
Purchase #3	$185.33	10.604%	$204.9824	$204.98	$205.00	$205.00
Purchase #4	$194.37	12.829%	$219.3057	$219.31	$219.30	$219.30
Purchase #5	$122.65	4.279%	$127.8982	$127.90	$127.90	$127.90
Purchase #6	$127.43	12.873%	$143.8341	$143.83	$143.85	$143.80
Purchase #7	$63.73	8.670%	$69.2554	$69.26	$69.25	$69.30
7 purchase totals =	$852.78		$932.3767	$932.38	$932.40	$932.40