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	$49.92	3.169%	$51.502	$51.50	$51.50	$51.50
Purchase #2	$176.67	5.482%	$186.355	$186.36	$186.35	$186.40
Purchase #3	$164.51	13.226%	$186.2681	$186.27	$186.25	$186.30
Purchase #4	$159.26	13.589%	$180.9018	$180.90	$180.90	$180.90
Purchase #5	$29.75	5.223%	$31.3038	$31.30	$31.30	$31.30
Purchase #6	$98.94	12.417%	$111.2254	$111.23	$111.25	$111.20
Purchase #7	$18.55	4.203%	$19.3297	$19.33	$19.35	$19.30
7 purchase totals =	$697.60		$766.8858	$766.89	$766.90	$766.90