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	$86.85	5.680%	$91.7831	$91.78	$91.80	$91.80
Purchase #2	$131.41	11.874%	$147.0136	$147.01	$147.00	$147.00
Purchase #3	$84.58	7.338%	$90.7865	$90.79	$90.80	$90.80
Purchase #4	$165.52	12.158%	$185.6439	$185.64	$185.65	$185.60
Purchase #5	$68.66	3.809%	$71.2753	$71.28	$71.30	$71.30
Purchase #6	$44.87	12.207%	$50.3473	$50.35	$50.35	$50.30
Purchase #7	$248.55	6.231%	$264.0372	$264.04	$264.05	$264.00
7 purchase totals =	$830.44		$900.8869	$900.89	$900.95	$900.80