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	$113.87	5.394%	$120.0121	$120.01	$120.00	$120.00
Purchase #2	$223.51	4.424%	$233.3981	$233.40	$233.40	$233.40
Purchase #3	$159.45	13.180%	$180.4655	$180.47	$180.45	$180.50
Purchase #4	$243.51	9.797%	$267.3667	$267.37	$267.35	$267.40
Purchase #5	$27.67	13.675%	$31.4539	$31.45	$31.45	$31.50
Purchase #6	$137.98	4.142%	$143.6951	$143.70	$143.70	$143.70
Purchase #7	$47.34	10.753%	$52.4305	$52.43	$52.45	$52.40
7 purchase totals =	$953.33		$1,028.8219	$1,028.83	$1,028.80	$1,028.90