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	$233.41	4.311%	$243.4723	$243.47	$243.45	$243.50
Purchase #2	$136.97	10.572%	$151.4505	$151.45	$151.45	$151.50
Purchase #3	$171.87	11.568%	$191.7519	$191.75	$191.75	$191.80
Purchase #4	$43.91	11.782%	$49.0835	$49.08	$49.10	$49.10
Purchase #5	$153.61	7.800%	$165.5916	$165.59	$165.60	$165.60
Purchase #6	$66.66	9.688%	$73.118	$73.12	$73.10	$73.10
Purchase #7	$203.37	4.676%	$212.8796	$212.88	$212.90	$212.90
7 purchase totals =	$1,009.80		$1,087.3474	$1,087.34	$1,087.35	$1,087.50