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	$19.34	5.673%	$20.4372	$20.44	$20.45	$20.40
Purchase #2	$56.29	6.315%	$59.8447	$59.84	$59.85	$59.80
Purchase #3	$170.90	9.205%	$186.6313	$186.63	$186.65	$186.60
Purchase #4	$242.60	8.840%	$264.0458	$264.05	$264.05	$264.00
Purchase #5	$157.57	4.755%	$165.0625	$165.06	$165.05	$165.10
Purchase #6	$231.82	11.607%	$258.7273	$258.73	$258.75	$258.70
Purchase #7	$125.89	13.444%	$142.8147	$142.81	$142.80	$142.80
7 purchase totals =	$1,004.41		$1,097.5635	$1,097.56	$1,097.60	$1,097.40