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	$120.27	8.600%	$130.6132	$130.61	$130.60	$130.60
Purchase #2	$31.59	3.475%	$32.6878	$32.69	$32.70	$32.70
Purchase #3	$138.42	13.338%	$156.8825	$156.88	$156.90	$156.90
Purchase #4	$41.92	9.187%	$45.7712	$45.77	$45.75	$45.80
Purchase #5	$134.62	9.216%	$147.0266	$147.03	$147.05	$147.00
Purchase #6	$243.68	8.633%	$264.7169	$264.72	$264.70	$264.70
Purchase #7	$211.28	6.189%	$224.3561	$224.36	$224.35	$224.40
7 purchase totals =	$921.78		$1,002.0543	$1,002.06	$1,002.05	$1,002.10