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	$14.57	5.700%	$15.4005	$15.40	$15.40	$15.40
Purchase #2	$246.77	7.851%	$266.1439	$266.14	$266.15	$266.10
Purchase #3	$91.60	12.821%	$103.344	$103.34	$103.35	$103.30
Purchase #4	$172.34	5.583%	$181.9617	$181.96	$181.95	$182.00
Purchase #5	$52.63	12.140%	$59.0193	$59.02	$59.00	$59.00
Purchase #6	$162.81	9.504%	$178.2835	$178.28	$178.30	$178.30
Purchase #7	$191.77	3.414%	$198.317	$198.32	$198.30	$198.30
7 purchase totals =	$932.49		$1,002.4699	$1,002.46	$1,002.45	$1,002.40