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	$82.29	11.219%	$91.5221	$91.52	$91.50	$91.50
Purchase #2	$21.74	5.500%	$22.9357	$22.94	$22.95	$22.90
Purchase #3	$53.86	4.555%	$56.3133	$56.31	$56.30	$56.30
Purchase #4	$190.77	11.871%	$213.4163	$213.42	$213.40	$213.40
Purchase #5	$104.81	10.181%	$115.4807	$115.48	$115.50	$115.50
Purchase #6	$109.85	11.848%	$122.865	$122.87	$122.85	$122.90
Purchase #7	$38.52	12.126%	$43.1909	$43.19	$43.20	$43.20
7 purchase totals =	$601.84		$665.7240	$665.73	$665.70	$665.70