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	$226.36	12.404%	$254.4377	$254.44	$254.45	$254.40
Purchase #2	$82.33	11.240%	$91.5839	$91.58	$91.60	$91.60
Purchase #3	$43.87	8.484%	$47.5919	$47.59	$47.60	$47.60
Purchase #4	$196.84	12.827%	$222.0887	$222.09	$222.10	$222.10
Purchase #5	$218.67	5.842%	$231.4447	$231.44	$231.45	$231.40
Purchase #6	$79.89	13.808%	$90.9212	$90.92	$90.90	$90.90
Purchase #7	$77.44	10.181%	$85.3242	$85.32	$85.30	$85.30
7 purchase totals =	$925.40		$1,023.3923	$1,023.38	$1,023.40	$1,023.30