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	$171.93	6.867%	$183.7364	$183.74	$183.75	$183.70
Purchase #2	$92.77	8.635%	$100.7807	$100.78	$100.80	$100.80
Purchase #3	$35.54	13.590%	$40.3699	$40.37	$40.35	$40.40
Purchase #4	$73.25	9.526%	$80.2278	$80.23	$80.25	$80.20
Purchase #5	$239.51	10.843%	$265.4801	$265.48	$265.50	$265.50
Purchase #6	$180.70	3.175%	$186.4372	$186.44	$186.45	$186.40
Purchase #7	$90.33	9.783%	$99.167	$99.17	$99.15	$99.20
7 purchase totals =	$884.03		$956.1991	$956.21	$956.25	$956.20