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	$25.34	6.399%	$26.9615	$26.96	$26.95	$27.00
Purchase #2	$87.96	8.353%	$95.3073	$95.31	$95.30	$95.30
Purchase #3	$230.64	8.792%	$250.9179	$250.92	$250.90	$250.90
Purchase #4	$80.54	11.162%	$89.5299	$89.53	$89.55	$89.50
Purchase #5	$7.25	9.823%	$7.9622	$7.96	$7.95	$8.00
Purchase #6	$174.91	9.696%	$191.8693	$191.87	$191.85	$191.90
Purchase #7	$80.42	12.790%	$90.7057	$90.71	$90.70	$90.70
7 purchase totals =	$687.06		$753.2538	$753.26	$753.20	$753.30