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	$37.81	12.729%	$42.6228	$42.62	$42.60	$42.60
Purchase #2	$60.78	11.768%	$67.9326	$67.93	$67.95	$67.90
Purchase #3	$241.93	7.165%	$259.2643	$259.26	$259.25	$259.30
Purchase #4	$33.97	13.607%	$38.5923	$38.59	$38.60	$38.60
Purchase #5	$235.56	12.109%	$264.084	$264.08	$264.10	$264.10
Purchase #6	$165.49	13.575%	$187.9553	$187.96	$187.95	$188.00
Purchase #7	$81.91	6.139%	$86.9385	$86.94	$86.95	$86.90
7 purchase totals =	$857.45		$947.3898	$947.38	$947.40	$947.40