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	$38.59	11.517%	$43.0344	$43.03	$43.05	$43.00
Purchase #2	$111.71	13.805%	$127.1316	$127.13	$127.15	$127.10
Purchase #3	$64.84	5.863%	$68.6416	$68.64	$68.65	$68.60
Purchase #4	$20.70	10.303%	$22.8327	$22.83	$22.85	$22.80
Purchase #5	$229.98	5.801%	$243.3211	$243.32	$243.30	$243.30
Purchase #6	$80.59	4.116%	$83.9071	$83.91	$83.90	$83.90
Purchase #7	$100.86	3.437%	$104.3266	$104.33	$104.35	$104.30
7 purchase totals =	$647.27		$693.1951	$693.19	$693.25	$693.00