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	$212.75	5.485%	$224.4193	$224.42	$224.40	$224.40
Purchase #2	$86.72	9.825%	$95.2402	$95.24	$95.25	$95.20
Purchase #3	$174.59	13.820%	$198.7183	$198.72	$198.70	$198.70
Purchase #4	$48.86	3.266%	$50.4558	$50.46	$50.45	$50.50
Purchase #5	$42.89	6.827%	$45.8181	$45.82	$45.80	$45.80
Purchase #6	$207.31	6.556%	$220.9012	$220.90	$220.90	$220.90
Purchase #7	$91.56	9.635%	$100.3818	$100.38	$100.40	$100.40
7 purchase totals =	$864.68		$935.9347	$935.94	$935.90	$935.90