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	$83.53	7.721%	$89.9794	$89.98	$90.00	$90.00
Purchase #2	$67.50	3.503%	$69.8645	$69.86	$69.85	$69.90
Purchase #3	$63.31	6.380%	$67.3492	$67.35	$67.35	$67.30
Purchase #4	$230.83	4.156%	$240.4233	$240.42	$240.40	$240.40
Purchase #5	$122.46	10.821%	$135.7114	$135.71	$135.70	$135.70
Purchase #6	$239.85	10.688%	$265.4852	$265.49	$265.50	$265.50
Purchase #7	$200.60	12.324%	$225.3219	$225.32	$225.30	$225.30
7 purchase totals =	$1,008.08		$1,094.1349	$1,094.13	$1,094.10	$1,094.10