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	$86.68	3.753%	$89.9331	$89.93	$89.95	$89.90
Purchase #2	$31.27	3.734%	$32.4376	$32.44	$32.45	$32.40
Purchase #3	$24.32	6.582%	$25.9207	$25.92	$25.90	$25.90
Purchase #4	$222.99	8.612%	$242.1939	$242.19	$242.20	$242.20
Purchase #5	$51.50	8.547%	$55.9017	$55.90	$55.90	$55.90
Purchase #6	$179.43	13.526%	$203.6997	$203.70	$203.70	$203.70
Purchase #7	$174.84	6.278%	$185.8165	$185.82	$185.80	$185.80
7 purchase totals =	$771.03		$835.9032	$835.90	$835.90	$835.80