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	$183.82	3.227%	$189.7519	$189.75	$189.75	$189.80
Purchase #2	$11.86	13.501%	$13.4612	$13.46	$13.45	$13.50
Purchase #3	$152.94	12.371%	$171.8602	$171.86	$171.85	$171.90
Purchase #4	$73.65	12.568%	$82.9063	$82.91	$82.90	$82.90
Purchase #5	$18.72	6.830%	$19.9986	$20.00	$20.00	$20.00
Purchase #6	$63.90	5.793%	$67.6017	$67.60	$67.60	$67.60
Purchase #7	$5.66	11.640%	$6.3188	$6.32	$6.30	$6.30
7 purchase totals =	$510.55		$551.8987	$551.90	$551.85	$552.00