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	$249.39	8.150%	$269.7153	$269.72	$269.70	$269.70
Purchase #2	$71.38	13.644%	$81.1191	$81.12	$81.10	$81.10
Purchase #3	$33.41	13.263%	$37.8412	$37.84	$37.85	$37.80
Purchase #4	$162.45	7.188%	$174.1269	$174.13	$174.15	$174.10
Purchase #5	$32.27	4.840%	$33.8319	$33.83	$33.85	$33.80
Purchase #6	$35.54	7.402%	$38.1707	$38.17	$38.15	$38.20
Purchase #7	$99.53	7.853%	$107.3461	$107.35	$107.35	$107.30
7 purchase totals =	$683.97		$742.1512	$742.16	$742.15	$742.00