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	$17.91	10.812%	$19.8464	$19.85	$19.85	$19.80
Purchase #2	$223.48	7.620%	$240.5092	$240.51	$240.50	$240.50
Purchase #3	$21.45	9.263%	$23.4369	$23.44	$23.45	$23.40
Purchase #4	$196.54	13.765%	$223.5937	$223.59	$223.60	$223.60
Purchase #5	$118.30	13.786%	$134.6088	$134.61	$134.60	$134.60
Purchase #6	$250.93	8.508%	$272.2791	$272.28	$272.30	$272.30
Purchase #7	$73.84	11.227%	$82.13	$82.13	$82.15	$82.10
7 purchase totals =	$902.45		$996.4041	$996.41	$996.45	$996.30