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	$131.33	4.183%	$136.8235	$136.82	$136.80	$136.80
Purchase #2	$38.55	11.507%	$42.9859	$42.99	$43.00	$43.00
Purchase #3	$44.89	7.207%	$48.1252	$48.13	$48.15	$48.10
Purchase #4	$243.38	13.353%	$275.8785	$275.88	$275.90	$275.90
Purchase #5	$65.96	9.442%	$72.1879	$72.19	$72.20	$72.20
Purchase #6	$134.54	12.673%	$151.5903	$151.59	$151.60	$151.60
Purchase #7	$108.31	6.245%	$115.074	$115.07	$115.05	$115.10
7 purchase totals =	$766.96		$842.6653	$842.67	$842.70	$842.70