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	$77.89	9.632%	$85.3924	$85.39	$85.40	$85.40
Purchase #2	$151.64	11.742%	$169.4456	$169.45	$169.45	$169.40
Purchase #3	$206.25	11.652%	$230.2823	$230.28	$230.30	$230.30
Purchase #4	$234.88	4.254%	$244.8718	$244.87	$244.85	$244.90
Purchase #5	$50.80	11.619%	$56.7025	$56.70	$56.70	$56.70
Purchase #6	$65.56	12.427%	$73.7071	$73.71	$73.70	$73.70
Purchase #7	$83.70	6.694%	$89.3029	$89.30	$89.30	$89.30
7 purchase totals =	$870.72		$949.7046	$949.70	$949.70	$949.70