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	$55.42	9.224%	$60.5319	$60.53	$60.55	$60.50
Purchase #2	$100.77	10.801%	$111.6542	$111.65	$111.65	$111.70
Purchase #3	$102.81	10.393%	$113.495	$113.50	$113.50	$113.50
Purchase #4	$82.91	4.318%	$86.4901	$86.49	$86.50	$86.50
Purchase #5	$41.49	6.593%	$44.2254	$44.23	$44.25	$44.20
Purchase #6	$186.74	4.372%	$194.9043	$194.90	$194.90	$194.90
Purchase #7	$202.89	3.299%	$209.5833	$209.58	$209.60	$209.60
7 purchase totals =	$773.03		$820.8842	$820.88	$820.95	$820.90