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	$166.91	3.494%	$172.7418	$172.74	$172.75	$172.70
Purchase #2	$137.79	10.549%	$152.3255	$152.33	$152.35	$152.30
Purchase #3	$158.61	4.316%	$165.4556	$165.46	$165.45	$165.50
Purchase #4	$98.75	4.633%	$103.3251	$103.33	$103.35	$103.30
Purchase #5	$115.31	10.470%	$127.383	$127.38	$127.40	$127.40
Purchase #6	$98.76	8.268%	$106.9255	$106.93	$106.95	$106.90
Purchase #7	$5.82	10.694%	$6.4424	$6.44	$6.45	$6.40
7 purchase totals =	$781.95		$834.5989	$834.61	$834.70	$834.50