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	$135.76	4.245%	$141.523	$141.52	$141.50	$141.50
Purchase #2	$148.58	8.656%	$161.4411	$161.44	$161.45	$161.40
Purchase #3	$51.50	8.197%	$55.7215	$55.72	$55.70	$55.70
Purchase #4	$112.85	13.250%	$127.8026	$127.80	$127.80	$127.80
Purchase #5	$16.43	11.628%	$18.3405	$18.34	$18.35	$18.30
Purchase #6	$182.84	8.684%	$198.7178	$198.72	$198.70	$198.70
Purchase #7	$37.59	11.792%	$42.0226	$42.02	$42.00	$42.00
7 purchase totals =	$685.55		$745.5691	$745.56	$745.50	$745.40