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	$224.66	10.238%	$247.6607	$247.66	$247.65	$247.70
Purchase #2	$98.64	12.323%	$110.7954	$110.80	$110.80	$110.80
Purchase #3	$238.83	13.483%	$271.0314	$271.03	$271.05	$271.00
Purchase #4	$79.78	13.170%	$90.287	$90.29	$90.30	$90.30
Purchase #5	$171.57	4.349%	$179.0316	$179.03	$179.05	$179.00
Purchase #6	$29.90	4.864%	$31.3543	$31.35	$31.35	$31.40
Purchase #7	$53.72	11.404%	$59.8462	$59.85	$59.85	$59.80
7 purchase totals =	$897.10		$990.0066	$990.01	$990.05	$990.00