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	$201.91	5.404%	$212.8212	$212.82	$212.80	$212.80
Purchase #2	$148.91	10.830%	$165.037	$165.04	$165.05	$165.00
Purchase #3	$103.53	12.493%	$116.464	$116.46	$116.45	$116.50
Purchase #4	$56.58	5.804%	$59.8639	$59.86	$59.85	$59.90
Purchase #5	$152.57	9.479%	$167.0321	$167.03	$167.05	$167.00
Purchase #6	$73.92	7.292%	$79.3102	$79.31	$79.30	$79.30
Purchase #7	$35.58	8.659%	$38.6609	$38.66	$38.65	$38.70
7 purchase totals =	$773.00		$839.1893	$839.18	$839.15	$839.20