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	$138.29	6.565%	$147.3687	$147.37	$147.35	$147.40
Purchase #2	$137.74	9.180%	$150.3845	$150.38	$150.40	$150.40
Purchase #3	$35.37	4.764%	$37.055	$37.06	$37.05	$37.10
Purchase #4	$184.98	11.164%	$205.6312	$205.63	$205.65	$205.60
Purchase #5	$31.86	10.776%	$35.2932	$35.29	$35.30	$35.30
Purchase #6	$77.68	3.364%	$80.2932	$80.29	$80.30	$80.30
Purchase #7	$110.90	6.488%	$118.0952	$118.10	$118.10	$118.10
7 purchase totals =	$716.82		$774.1210	$774.12	$774.15	$774.20