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	$99.94	7.798%	$107.7333	$107.73	$107.75	$107.70
Purchase #2	$117.84	9.140%	$128.6106	$128.61	$128.60	$128.60
Purchase #3	$73.26	13.610%	$83.2307	$83.23	$83.25	$83.20
Purchase #4	$134.98	5.736%	$142.7225	$142.72	$142.70	$142.70
Purchase #5	$135.46	12.503%	$152.3966	$152.40	$152.40	$152.40
Purchase #6	$183.50	10.662%	$203.0648	$203.06	$203.05	$203.10
Purchase #7	$56.51	5.361%	$59.5395	$59.54	$59.55	$59.50
7 purchase totals =	$801.49		$877.2980	$877.29	$877.30	$877.20