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	$165.66	8.380%	$179.5423	$179.54	$179.55	$179.50
Purchase #2	$64.35	4.823%	$67.4536	$67.45	$67.45	$67.50
Purchase #3	$23.42	5.331%	$24.6685	$24.67	$24.65	$24.70
Purchase #4	$82.31	4.316%	$85.8625	$85.86	$85.85	$85.90
Purchase #5	$28.59	11.297%	$31.8198	$31.82	$31.80	$31.80
Purchase #6	$29.34	3.760%	$30.4432	$30.44	$30.45	$30.40
Purchase #7	$121.39	9.268%	$132.6404	$132.64	$132.65	$132.60
7 purchase totals =	$515.06		$552.4303	$552.42	$552.40	$552.40