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	$104.96	4.122%	$109.2865	$109.29	$109.30	$109.30
Purchase #2	$214.54	3.707%	$222.493	$222.49	$222.50	$222.50
Purchase #3	$196.51	11.334%	$218.7824	$218.78	$218.80	$218.80
Purchase #4	$185.83	5.490%	$196.0321	$196.03	$196.05	$196.00
Purchase #5	$191.27	3.524%	$198.0104	$198.01	$198.00	$198.00
Purchase #6	$97.37	12.250%	$109.2978	$109.30	$109.30	$109.30
Purchase #7	$30.92	12.362%	$34.7423	$34.74	$34.75	$34.70
7 purchase totals =	$1,021.40		$1,088.6445	$1,088.64	$1,088.70	$1,088.60