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	$106.95	12.308%	$120.1134	$120.11	$120.10	$120.10
Purchase #2	$76.25	8.753%	$82.9242	$82.92	$82.90	$82.90
Purchase #3	$204.33	5.267%	$215.0921	$215.09	$215.10	$215.10
Purchase #4	$203.52	12.195%	$228.3393	$228.34	$228.35	$228.30
Purchase #5	$242.77	13.499%	$275.5415	$275.54	$275.55	$275.50
Purchase #6	$22.53	11.108%	$25.0326	$25.03	$25.05	$25.00
Purchase #7	$93.71	7.674%	$100.9013	$100.90	$100.90	$100.90
7 purchase totals =	$950.06		$1,047.9444	$1,047.93	$1,047.95	$1,047.80