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	$36.46	10.797%	$40.3966	$40.40	$40.40	$40.40
Purchase #2	$243.89	6.132%	$258.8453	$258.85	$258.85	$258.80
Purchase #3	$33.71	6.210%	$35.8034	$35.80	$35.80	$35.80
Purchase #4	$66.60	5.222%	$70.0779	$70.08	$70.10	$70.10
Purchase #5	$126.87	12.237%	$142.3951	$142.40	$142.40	$142.40
Purchase #6	$40.67	6.171%	$43.1797	$43.18	$43.20	$43.20
Purchase #7	$246.62	8.570%	$267.7553	$267.76	$267.75	$267.80
7 purchase totals =	$794.82		$858.4533	$858.47	$858.50	$858.50