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	$235.48	5.691%	$248.8812	$248.88	$248.90	$248.90
Purchase #2	$27.40	8.120%	$29.6249	$29.62	$29.60	$29.60
Purchase #3	$240.81	5.180%	$253.284	$253.28	$253.30	$253.30
Purchase #4	$213.38	4.538%	$223.0632	$223.06	$223.05	$223.10
Purchase #5	$211.67	11.741%	$236.5222	$236.52	$236.50	$236.50
Purchase #6	$108.84	13.345%	$123.3647	$123.36	$123.35	$123.40
Purchase #7	$153.89	9.261%	$168.1418	$168.14	$168.15	$168.10
7 purchase totals =	$1,191.47		$1,282.8820	$1,282.86	$1,282.85	$1,282.90