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	$100.90	13.706%	$114.7294	$114.73	$114.75	$114.70
Purchase #2	$42.56	6.289%	$45.2366	$45.24	$45.25	$45.20
Purchase #3	$105.56	4.110%	$109.8985	$109.90	$109.90	$109.90
Purchase #4	$153.40	11.842%	$171.5656	$171.57	$171.55	$171.60
Purchase #5	$61.93	12.306%	$69.5511	$69.55	$69.55	$69.60
Purchase #6	$70.50	5.364%	$74.2816	$74.28	$74.30	$74.30
Purchase #7	$119.80	3.187%	$123.618	$123.62	$123.60	$123.60
7 purchase totals =	$654.65		$708.8808	$708.89	$708.90	$708.90