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	$74.69	6.759%	$79.7383	$79.74	$79.75	$79.70
Purchase #2	$170.64	10.547%	$188.6374	$188.64	$188.65	$188.60
Purchase #3	$31.43	12.557%	$35.3767	$35.38	$35.40	$35.40
Purchase #4	$122.61	7.131%	$131.3533	$131.35	$131.35	$131.40
Purchase #5	$141.74	13.253%	$160.5248	$160.52	$160.50	$160.50
Purchase #6	$150.72	3.394%	$155.8354	$155.84	$155.85	$155.80
Purchase #7	$37.89	11.305%	$42.1735	$42.17	$42.15	$42.20
7 purchase totals =	$729.72		$793.6394	$793.64	$793.65	$793.60