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	$131.94	6.454%	$140.4554	$140.46	$140.45	$140.50
Purchase #2	$236.56	6.432%	$251.7755	$251.78	$251.80	$251.80
Purchase #3	$30.64	9.687%	$33.6081	$33.61	$33.60	$33.60
Purchase #4	$81.59	11.254%	$90.7721	$90.77	$90.75	$90.80
Purchase #5	$95.73	3.834%	$99.4003	$99.40	$99.40	$99.40
Purchase #6	$142.25	4.205%	$148.2316	$148.23	$148.25	$148.20
Purchase #7	$139.26	11.804%	$155.6983	$155.70	$155.70	$155.70
7 purchase totals =	$857.97		$919.9413	$919.95	$919.95	$920.00