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	$22.30	11.681%	$24.9049	$24.90	$24.90	$24.90
Purchase #2	$115.71	13.115%	$130.8854	$130.89	$130.90	$130.90
Purchase #3	$67.56	13.253%	$76.5137	$76.51	$76.50	$76.50
Purchase #4	$21.86	11.641%	$24.4047	$24.40	$24.40	$24.40
Purchase #5	$18.80	8.861%	$20.4659	$20.47	$20.45	$20.50
Purchase #6	$65.37	10.524%	$72.2495	$72.25	$72.25	$72.20
Purchase #7	$135.75	11.444%	$151.2852	$151.29	$151.30	$151.30
7 purchase totals =	$447.35		$500.7093	$500.71	$500.70	$500.70