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	$15.50	12.190%	$17.3895	$17.39	$17.40	$17.40
Purchase #2	$140.83	4.317%	$146.9096	$146.91	$146.90	$146.90
Purchase #3	$162.97	11.796%	$182.1939	$182.19	$182.20	$182.20
Purchase #4	$180.93	6.526%	$192.7375	$192.74	$192.75	$192.70
Purchase #5	$82.83	7.684%	$89.1947	$89.19	$89.20	$89.20
Purchase #6	$50.85	6.847%	$54.3317	$54.33	$54.35	$54.30
Purchase #7	$179.40	4.478%	$187.4335	$187.43	$187.45	$187.40
7 purchase totals =	$813.31		$870.1904	$870.18	$870.25	$870.10