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	$175.35	11.790%	$196.0238	$196.02	$196.00	$196.00
Purchase #2	$18.95	9.419%	$20.7349	$20.73	$20.75	$20.70
Purchase #3	$137.65	3.276%	$142.1594	$142.16	$142.15	$142.20
Purchase #4	$75.68	10.102%	$83.3252	$83.33	$83.35	$83.30
Purchase #5	$31.55	12.181%	$35.3931	$35.39	$35.40	$35.40
Purchase #6	$137.83	8.788%	$149.9425	$149.94	$149.95	$149.90
Purchase #7	$212.84	12.259%	$238.9321	$238.93	$238.95	$238.90
7 purchase totals =	$789.85		$866.5110	$866.50	$866.55	$866.40