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	$40.89	3.107%	$42.1605	$42.16	$42.15	$42.20
Purchase #2	$201.45	4.113%	$209.7356	$209.74	$209.75	$209.70
Purchase #3	$241.35	8.360%	$261.5269	$261.53	$261.55	$261.50
Purchase #4	$146.85	12.738%	$165.5558	$165.56	$165.55	$165.60
Purchase #5	$57.68	4.575%	$60.3189	$60.32	$60.30	$60.30
Purchase #6	$93.56	8.277%	$101.304	$101.30	$101.30	$101.30
Purchase #7	$198.28	12.130%	$222.3314	$222.33	$222.35	$222.30
7 purchase totals =	$980.06		$1,062.9331	$1,062.94	$1,062.95	$1,062.90