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	$167.67	4.449%	$175.1296	$175.13	$175.15	$175.10
Purchase #2	$80.48	6.647%	$85.8295	$85.83	$85.85	$85.80
Purchase #3	$140.84	10.394%	$155.4789	$155.48	$155.50	$155.50
Purchase #4	$16.79	10.517%	$18.5558	$18.56	$18.55	$18.60
Purchase #5	$7.43	4.470%	$7.7621	$7.76	$7.75	$7.80
Purchase #6	$209.75	3.520%	$217.1332	$217.13	$217.15	$217.10
Purchase #7	$187.29	12.358%	$210.4353	$210.44	$210.45	$210.40
7 purchase totals =	$810.25		$870.3244	$870.33	$870.40	$870.30