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	$79.96	12.614%	$90.0462	$90.05	$90.05	$90.00
Purchase #2	$234.48	5.714%	$247.8782	$247.88	$247.90	$247.90
Purchase #3	$161.78	11.762%	$180.8086	$180.81	$180.80	$180.80
Purchase #4	$132.76	13.559%	$150.7609	$150.76	$150.75	$150.80
Purchase #5	$169.58	10.195%	$186.8687	$186.87	$186.85	$186.90
Purchase #6	$67.37	11.571%	$75.1654	$75.17	$75.15	$75.20
Purchase #7	$188.63	4.304%	$196.7486	$196.75	$196.75	$196.70
7 purchase totals =	$1,034.56		$1,128.2766	$1,128.29	$1,128.25	$1,128.30