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	$144.65	3.405%	$149.5753	$149.58	$149.60	$149.60
Purchase #2	$226.80	13.322%	$257.0143	$257.01	$257.00	$257.00
Purchase #3	$36.45	8.234%	$39.4513	$39.45	$39.45	$39.50
Purchase #4	$189.63	3.711%	$196.6672	$196.67	$196.65	$196.70
Purchase #5	$33.70	4.600%	$35.2502	$35.25	$35.25	$35.30
Purchase #6	$124.64	5.760%	$131.8193	$131.82	$131.80	$131.80
Purchase #7	$80.73	12.306%	$90.6646	$90.66	$90.65	$90.70
7 purchase totals =	$836.60		$900.4422	$900.44	$900.40	$900.60