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	$89.90	10.840%	$99.6452	$99.65	$99.65	$99.60
Purchase #2	$155.87	11.124%	$173.209	$173.21	$173.20	$173.20
Purchase #3	$62.53	11.437%	$69.6816	$69.68	$69.70	$69.70
Purchase #4	$169.56	13.662%	$192.7253	$192.73	$192.75	$192.70
Purchase #5	$81.76	6.283%	$86.897	$86.90	$86.90	$86.90
Purchase #6	$82.89	9.619%	$90.8632	$90.86	$90.85	$90.90
Purchase #7	$123.89	11.460%	$138.0878	$138.09	$138.10	$138.10
7 purchase totals =	$766.40		$851.1091	$851.12	$851.15	$851.10