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	$99.72	10.599%	$110.2893	$110.29	$110.30	$110.30
Purchase #2	$37.97	12.697%	$42.7911	$42.79	$42.80	$42.80
Purchase #3	$197.56	7.686%	$212.7445	$212.74	$212.75	$212.70
Purchase #4	$55.94	10.679%	$61.9138	$61.91	$61.90	$61.90
Purchase #5	$98.51	13.258%	$111.5705	$111.57	$111.55	$111.60
Purchase #6	$61.74	7.576%	$66.4174	$66.42	$66.40	$66.40
Purchase #7	$47.56	7.665%	$51.2055	$51.21	$51.20	$51.20
7 purchase totals =	$599.00		$656.9321	$656.93	$656.90	$656.90