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	$84.77	9.112%	$92.4942	$92.49	$92.50	$92.50
Purchase #2	$155.95	9.444%	$170.6779	$170.68	$170.70	$170.70
Purchase #3	$153.92	11.674%	$171.8886	$171.89	$171.90	$171.90
Purchase #4	$56.91	12.424%	$63.9805	$63.98	$64.00	$64.00
Purchase #5	$86.32	3.471%	$89.3162	$89.32	$89.30	$89.30
Purchase #6	$174.67	8.866%	$190.1562	$190.16	$190.15	$190.20
Purchase #7	$76.35	4.496%	$79.7827	$79.78	$79.80	$79.80
7 purchase totals =	$788.89		$858.2963	$858.30	$858.35	$858.40