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	$140.87	10.298%	$155.3768	$155.38	$155.40	$155.40
Purchase #2	$237.59	3.365%	$245.5849	$245.58	$245.60	$245.60
Purchase #3	$138.49	8.808%	$150.6882	$150.69	$150.70	$150.70
Purchase #4	$123.34	3.235%	$127.33	$127.33	$127.35	$127.30
Purchase #5	$20.60	4.751%	$21.5787	$21.58	$21.60	$21.60
Purchase #6	$63.82	12.217%	$71.6169	$71.62	$71.60	$71.60
Purchase #7	$98.80	6.302%	$105.0264	$105.03	$105.05	$105.00
7 purchase totals =	$823.51		$877.2019	$877.21	$877.30	$877.20