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	$84.67	4.644%	$88.6021	$88.60	$88.60	$88.60
Purchase #2	$147.45	12.857%	$166.4076	$166.41	$166.40	$166.40
Purchase #3	$144.80	9.454%	$158.4894	$158.49	$158.50	$158.50
Purchase #4	$5.70	7.371%	$6.1201	$6.12	$6.10	$6.10
Purchase #5	$79.34	12.609%	$89.344	$89.34	$89.35	$89.30
Purchase #6	$142.45	9.660%	$156.2107	$156.21	$156.20	$156.20
Purchase #7	$167.80	7.129%	$179.7625	$179.76	$179.75	$179.80
7 purchase totals =	$772.21		$844.9364	$844.93	$844.90	$844.90