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	$52.44	13.120%	$59.3201	$59.32	$59.30	$59.30
Purchase #2	$20.92	3.438%	$21.6392	$21.64	$21.65	$21.60
Purchase #3	$242.48	12.864%	$273.6726	$273.67	$273.65	$273.70
Purchase #4	$80.82	12.438%	$90.8724	$90.87	$90.85	$90.90
Purchase #5	$194.84	6.254%	$207.0253	$207.03	$207.05	$207.00
Purchase #6	$99.78	4.272%	$104.0426	$104.04	$104.05	$104.00
Purchase #7	$56.59	4.105%	$58.913	$58.91	$58.90	$58.90
7 purchase totals =	$747.87		$815.4852	$815.48	$815.45	$815.40