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	$15.68	9.380%	$17.1508	$17.15	$17.15	$17.20
Purchase #2	$246.60	3.253%	$254.6219	$254.62	$254.60	$254.60
Purchase #3	$79.30	12.710%	$89.379	$89.38	$89.40	$89.40
Purchase #4	$105.50	11.857%	$118.0091	$118.01	$118.00	$118.00
Purchase #5	$227.64	7.131%	$243.873	$243.87	$243.85	$243.90
Purchase #6	$28.44	7.188%	$30.4843	$30.48	$30.50	$30.50
Purchase #7	$235.79	6.172%	$250.343	$250.34	$250.35	$250.30
7 purchase totals =	$938.95		$1,003.8611	$1,003.85	$1,003.85	$1,003.90