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	$235.34	9.798%	$258.3986	$258.40	$258.40	$258.40
Purchase #2	$171.59	6.208%	$182.2423	$182.24	$182.25	$182.20
Purchase #3	$227.90	10.457%	$251.7315	$251.73	$251.75	$251.70
Purchase #4	$79.96	3.692%	$82.9121	$82.91	$82.90	$82.90
Purchase #5	$91.52	13.482%	$103.8587	$103.86	$103.85	$103.90
Purchase #6	$188.36	8.777%	$204.8924	$204.89	$204.90	$204.90
Purchase #7	$81.26	11.848%	$90.8877	$90.89	$90.90	$90.90
7 purchase totals =	$1,075.93		$1,174.9233	$1,174.92	$1,174.95	$1,174.90