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	$91.63	12.382%	$102.9756	$102.98	$103.00	$103.00
Purchase #2	$49.27	12.590%	$55.4731	$55.47	$55.45	$55.50
Purchase #3	$214.96	7.671%	$231.4496	$231.45	$231.45	$231.40
Purchase #4	$72.49	13.751%	$82.4581	$82.46	$82.45	$82.50
Purchase #5	$166.69	13.676%	$189.4865	$189.49	$189.50	$189.50
Purchase #6	$175.66	4.158%	$182.9639	$182.96	$182.95	$183.00
Purchase #7	$219.76	10.177%	$242.125	$242.13	$242.15	$242.10
7 purchase totals =	$990.46		$1,086.9318	$1,086.94	$1,086.95	$1,087.00