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	$88.96	11.179%	$98.9048	$98.90	$98.90	$98.90
Purchase #2	$148.67	3.266%	$153.5256	$153.53	$153.55	$153.50
Purchase #3	$10.85	9.106%	$11.838	$11.84	$11.85	$11.80
Purchase #4	$150.50	8.144%	$162.7567	$162.76	$162.75	$162.80
Purchase #5	$152.35	11.422%	$169.7514	$169.75	$169.75	$169.80
Purchase #6	$170.28	11.799%	$190.3713	$190.37	$190.35	$190.40
Purchase #7	$105.90	6.396%	$112.6734	$112.67	$112.65	$112.70
7 purchase totals =	$827.51		$899.8212	$899.82	$899.80	$899.90