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	$37.35	8.692%	$40.5965	$40.60	$40.60	$40.60
Purchase #2	$106.73	7.661%	$114.9066	$114.91	$114.90	$114.90
Purchase #3	$236.47	3.849%	$245.5717	$245.57	$245.55	$245.60
Purchase #4	$136.66	11.230%	$152.0069	$152.01	$152.00	$152.00
Purchase #5	$152.98	10.573%	$169.1546	$169.15	$169.15	$169.20
Purchase #6	$160.37	6.372%	$170.5888	$170.59	$170.60	$170.60
Purchase #7	$185.70	13.501%	$210.7714	$210.77	$210.75	$210.80
7 purchase totals =	$1,016.26		$1,103.5965	$1,103.60	$1,103.55	$1,103.70