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	$5.89	10.740%	$6.5226	$6.52	$6.50	$6.50
Purchase #2	$69.56	11.568%	$77.6067	$77.61	$77.60	$77.60
Purchase #3	$64.74	11.283%	$72.0446	$72.04	$72.05	$72.00
Purchase #4	$82.99	4.347%	$86.5976	$86.60	$86.60	$86.60
Purchase #5	$190.25	6.447%	$202.5154	$202.52	$202.50	$202.50
Purchase #6	$241.27	12.533%	$271.5084	$271.51	$271.50	$271.50
Purchase #7	$153.48	11.109%	$170.5301	$170.53	$170.55	$170.50
7 purchase totals =	$808.18		$887.3254	$887.33	$887.30	$887.20