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	$171.74	13.167%	$194.353	$194.35	$194.35	$194.40
Purchase #2	$236.76	11.747%	$264.5722	$264.57	$264.55	$264.60
Purchase #3	$70.64	10.721%	$78.2133	$78.21	$78.20	$78.20
Purchase #4	$218.57	9.242%	$238.7702	$238.77	$238.75	$238.80
Purchase #5	$91.94	11.457%	$102.4736	$102.47	$102.45	$102.50
Purchase #6	$25.67	11.846%	$28.7109	$28.71	$28.70	$28.70
Purchase #7	$76.51	12.489%	$86.0653	$86.07	$86.05	$86.10
7 purchase totals =	$891.83		$993.1585	$993.15	$993.05	$993.30