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	$40.46	11.262%	$45.0166	$45.02	$45.00	$45.00
Purchase #2	$227.76	12.665%	$256.6058	$256.61	$256.60	$256.60
Purchase #3	$7.87	5.262%	$8.2841	$8.28	$8.30	$8.30
Purchase #4	$50.90	12.827%	$57.4289	$57.43	$57.45	$57.40
Purchase #5	$199.73	6.849%	$213.4095	$213.41	$213.40	$213.40
Purchase #6	$22.78	10.169%	$25.0965	$25.10	$25.10	$25.10
Purchase #7	$59.58	13.134%	$67.4052	$67.41	$67.40	$67.40
7 purchase totals =	$609.08		$673.2466	$673.26	$673.25	$673.20