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	$78.38	3.786%	$81.3475	$81.35	$81.35	$81.30
Purchase #2	$173.97	9.760%	$190.9495	$190.95	$190.95	$190.90
Purchase #3	$20.73	10.557%	$22.9185	$22.92	$22.90	$22.90
Purchase #4	$197.73	12.479%	$222.4047	$222.40	$222.40	$222.40
Purchase #5	$99.88	9.765%	$109.6333	$109.63	$109.65	$109.60
Purchase #6	$166.75	12.353%	$187.3486	$187.35	$187.35	$187.30
Purchase #7	$136.87	4.182%	$142.5939	$142.59	$142.60	$142.60
7 purchase totals =	$874.31		$957.1960	$957.19	$957.20	$957.00