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	$89.84	10.741%	$99.4897	$99.49	$99.50	$99.50
Purchase #2	$225.85	12.669%	$254.4629	$254.46	$254.45	$254.50
Purchase #3	$168.37	8.659%	$182.9492	$182.95	$182.95	$182.90
Purchase #4	$29.95	5.271%	$31.5287	$31.53	$31.55	$31.50
Purchase #5	$54.99	7.598%	$59.1681	$59.17	$59.15	$59.20
Purchase #6	$73.72	12.282%	$82.7743	$82.77	$82.75	$82.80
Purchase #7	$28.43	13.727%	$32.3326	$32.33	$32.35	$32.30
7 purchase totals =	$671.15		$742.7055	$742.70	$742.70	$742.70