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	$89.31	12.867%	$100.8015	$100.80	$100.80	$100.80
Purchase #2	$44.61	12.554%	$50.2103	$50.21	$50.20	$50.20
Purchase #3	$71.83	6.763%	$76.6879	$76.69	$76.70	$76.70
Purchase #4	$175.87	11.655%	$196.3676	$196.37	$196.35	$196.40
Purchase #5	$73.44	6.544%	$78.2459	$78.25	$78.25	$78.20
Purchase #6	$123.73	11.336%	$137.756	$137.76	$137.75	$137.80
Purchase #7	$174.43	6.218%	$185.2761	$185.28	$185.30	$185.30
7 purchase totals =	$753.22		$825.3453	$825.36	$825.35	$825.40