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	$196.83	13.620%	$223.6382	$223.64	$223.65	$223.60
Purchase #2	$21.82	4.339%	$22.7668	$22.77	$22.75	$22.80
Purchase #3	$152.58	13.629%	$173.3751	$173.38	$173.40	$173.40
Purchase #4	$171.59	4.441%	$179.2103	$179.21	$179.20	$179.20
Purchase #5	$31.42	12.553%	$35.3642	$35.36	$35.35	$35.40
Purchase #6	$76.61	6.165%	$81.333	$81.33	$81.35	$81.30
Purchase #7	$250.93	13.259%	$284.2008	$284.20	$284.20	$284.20
7 purchase totals =	$901.78		$999.8884	$999.89	$999.90	$999.90