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	$122.75	7.478%	$131.9292	$131.93	$131.95	$131.90
Purchase #2	$226.76	11.595%	$253.0528	$253.05	$253.05	$253.10
Purchase #3	$151.34	13.463%	$171.7149	$171.71	$171.70	$171.70
Purchase #4	$204.57	9.310%	$223.6155	$223.62	$223.60	$223.60
Purchase #5	$35.92	4.383%	$37.4944	$37.49	$37.50	$37.50
Purchase #6	$142.64	12.223%	$160.0749	$160.07	$160.05	$160.10
Purchase #7	$110.50	10.741%	$122.3688	$122.37	$122.35	$122.40
7 purchase totals =	$994.48		$1,100.2505	$1,100.24	$1,100.20	$1,100.30