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	$245.79	11.447%	$273.9256	$273.93	$273.95	$273.90
Purchase #2	$47.44	11.489%	$52.8904	$52.89	$52.90	$52.90
Purchase #3	$132.70	11.825%	$148.3918	$148.39	$148.40	$148.40
Purchase #4	$19.63	6.383%	$20.883	$20.88	$20.90	$20.90
Purchase #5	$48.69	13.464%	$55.2456	$55.25	$55.25	$55.20
Purchase #6	$94.27	11.779%	$105.3741	$105.37	$105.35	$105.40
Purchase #7	$127.42	9.489%	$139.5109	$139.51	$139.50	$139.50
7 purchase totals =	$715.94		$796.2214	$796.22	$796.25	$796.20