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	$167.74	12.387%	$188.518	$188.52	$188.50	$188.50
Purchase #2	$191.88	3.816%	$199.2021	$199.20	$199.20	$199.20
Purchase #3	$195.84	13.699%	$222.6681	$222.67	$222.65	$222.70
Purchase #4	$97.99	6.539%	$104.3976	$104.40	$104.40	$104.40
Purchase #5	$170.31	9.153%	$185.8985	$185.90	$185.90	$185.90
Purchase #6	$38.93	11.779%	$43.5156	$43.52	$43.50	$43.50
Purchase #7	$109.66	3.587%	$113.5935	$113.59	$113.60	$113.60
7 purchase totals =	$972.35		$1,057.7934	$1,057.80	$1,057.75	$1,057.80