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	$93.91	6.147%	$99.6826	$99.68	$99.70	$99.70
Purchase #2	$87.36	11.414%	$97.3313	$97.33	$97.35	$97.30
Purchase #3	$189.43	13.742%	$215.4615	$215.46	$215.45	$215.50
Purchase #4	$167.91	13.845%	$191.1571	$191.16	$191.15	$191.20
Purchase #5	$139.54	4.123%	$145.2932	$145.29	$145.30	$145.30
Purchase #6	$71.61	5.502%	$75.55	$75.55	$75.55	$75.60
Purchase #7	$246.95	3.816%	$256.3736	$256.37	$256.35	$256.40
7 purchase totals =	$996.71		$1,080.8493	$1,080.84	$1,080.85	$1,081.00