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	$35.76	11.502%	$39.8731	$39.87	$39.85	$39.90
Purchase #2	$39.89	7.355%	$42.8239	$42.82	$42.80	$42.80
Purchase #3	$17.65	3.266%	$18.2264	$18.23	$18.25	$18.20
Purchase #4	$143.58	8.378%	$155.6091	$155.61	$155.60	$155.60
Purchase #5	$111.82	3.852%	$116.1273	$116.13	$116.15	$116.10
Purchase #6	$25.37	10.657%	$28.0737	$28.07	$28.05	$28.10
Purchase #7	$94.44	7.756%	$101.7648	$101.76	$101.75	$101.80
7 purchase totals =	$468.51		$502.4983	$502.49	$502.45	$502.50