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	$121.95	11.683%	$136.1974	$136.20	$136.20	$136.20
Purchase #2	$45.81	3.764%	$47.5343	$47.53	$47.55	$47.50
Purchase #3	$158.50	7.793%	$170.8519	$170.85	$170.85	$170.90
Purchase #4	$136.56	11.708%	$152.5484	$152.55	$152.55	$152.50
Purchase #5	$116.87	13.206%	$132.3039	$132.30	$132.30	$132.30
Purchase #6	$222.77	12.339%	$250.2576	$250.26	$250.25	$250.30
Purchase #7	$243.52	10.834%	$269.903	$269.90	$269.90	$269.90
7 purchase totals =	$1,045.98		$1,159.5965	$1,159.59	$1,159.60	$1,159.60