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	$25.31	7.153%	$27.1204	$27.12	$27.10	$27.10
Purchase #2	$72.76	4.444%	$75.9935	$75.99	$76.00	$76.00
Purchase #3	$209.40	13.527%	$237.7255	$237.73	$237.75	$237.70
Purchase #4	$123.78	6.157%	$131.4011	$131.40	$131.40	$131.40
Purchase #5	$69.29	3.154%	$71.4754	$71.48	$71.50	$71.50
Purchase #6	$76.41	9.334%	$83.5421	$83.54	$83.55	$83.50
Purchase #7	$56.37	8.475%	$61.1474	$61.15	$61.15	$61.10
7 purchase totals =	$633.32		$688.4054	$688.41	$688.45	$688.30