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	$250.87	5.562%	$264.8234	$264.82	$264.80	$264.80
Purchase #2	$47.78	12.323%	$53.6679	$53.67	$53.65	$53.70
Purchase #3	$123.79	3.495%	$128.1165	$128.12	$128.10	$128.10
Purchase #4	$99.94	4.847%	$104.7841	$104.78	$104.80	$104.80
Purchase #5	$231.67	5.347%	$244.0574	$244.06	$244.05	$244.10
Purchase #6	$83.96	12.606%	$94.544	$94.54	$94.55	$94.50
Purchase #7	$102.32	10.457%	$113.0196	$113.02	$113.00	$113.00
7 purchase totals =	$940.33		$1,003.0129	$1,003.01	$1,002.95	$1,003.00