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	$131.91	11.275%	$146.7829	$146.78	$146.80	$146.80
Purchase #2	$172.44	9.532%	$188.877	$188.88	$188.90	$188.90
Purchase #3	$74.56	7.769%	$80.3526	$80.35	$80.35	$80.40
Purchase #4	$221.68	10.752%	$245.515	$245.52	$245.50	$245.50
Purchase #5	$66.37	3.314%	$68.5695	$68.57	$68.55	$68.60
Purchase #6	$44.25	3.715%	$45.8939	$45.89	$45.90	$45.90
Purchase #7	$146.81	7.861%	$158.3507	$158.35	$158.35	$158.40
7 purchase totals =	$858.02		$934.3416	$934.34	$934.35	$934.50