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	$20.28	7.675%	$21.8365	$21.84	$21.85	$21.80
Purchase #2	$46.98	11.352%	$52.3132	$52.31	$52.30	$52.30
Purchase #3	$47.35	10.516%	$52.3293	$52.33	$52.35	$52.30
Purchase #4	$52.99	11.465%	$59.0653	$59.07	$59.05	$59.10
Purchase #5	$95.86	11.269%	$106.6625	$106.66	$106.65	$106.70
Purchase #6	$117.41	11.553%	$130.9744	$130.97	$130.95	$131.00
Purchase #7	$75.58	10.783%	$83.7298	$83.73	$83.75	$83.70
7 purchase totals =	$456.45		$506.9110	$506.91	$506.90	$506.90