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	$78.68	3.528%	$81.4558	$81.46	$81.45	$81.50
Purchase #2	$77.72	13.570%	$88.2666	$88.27	$88.25	$88.30
Purchase #3	$40.64	3.405%	$42.0238	$42.02	$42.00	$42.00
Purchase #4	$220.74	3.350%	$228.1348	$228.13	$228.15	$228.10
Purchase #5	$183.84	9.617%	$201.5199	$201.52	$201.50	$201.50
Purchase #6	$79.48	7.243%	$85.2367	$85.24	$85.25	$85.20
Purchase #7	$39.94	6.635%	$42.59	$42.59	$42.60	$42.60
7 purchase totals =	$721.04		$769.2276	$769.23	$769.20	$769.20