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	$56.42	5.419%	$59.4774	$59.48	$59.50	$59.50
Purchase #2	$173.35	3.779%	$179.9009	$179.90	$179.90	$179.90
Purchase #3	$234.52	5.688%	$247.8595	$247.86	$247.85	$247.90
Purchase #4	$73.96	3.342%	$76.4317	$76.43	$76.45	$76.40
Purchase #5	$51.52	12.306%	$57.8601	$57.86	$57.85	$57.90
Purchase #6	$110.33	6.374%	$117.3624	$117.36	$117.35	$117.40
Purchase #7	$144.39	6.547%	$153.8432	$153.84	$153.85	$153.80
7 purchase totals =	$844.49		$892.7352	$892.73	$892.75	$892.80