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	$82.46	7.807%	$88.8977	$88.90	$88.90	$88.90
Purchase #2	$168.42	9.138%	$183.8102	$183.81	$183.80	$183.80
Purchase #3	$200.78	4.769%	$210.3552	$210.36	$210.35	$210.40
Purchase #4	$88.71	3.601%	$91.9044	$91.90	$91.90	$91.90
Purchase #5	$26.87	5.601%	$28.375	$28.38	$28.40	$28.40
Purchase #6	$51.86	9.737%	$56.9096	$56.91	$56.90	$56.90
Purchase #7	$145.51	9.587%	$159.46	$159.46	$159.45	$159.50
7 purchase totals =	$764.61		$819.7121	$819.72	$819.70	$819.80