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	$150.56	13.818%	$171.3644	$171.36	$171.35	$171.40
Purchase #2	$98.58	5.860%	$104.3568	$104.36	$104.35	$104.40
Purchase #3	$93.30	4.520%	$97.5172	$97.52	$97.50	$97.50
Purchase #4	$91.78	9.379%	$100.388	$100.39	$100.40	$100.40
Purchase #5	$140.48	4.449%	$146.73	$146.73	$146.75	$146.70
Purchase #6	$141.57	11.501%	$157.852	$157.85	$157.85	$157.90
Purchase #7	$55.57	9.457%	$60.8253	$60.83	$60.85	$60.80
7 purchase totals =	$771.84		$839.0337	$839.04	$839.05	$839.10