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	$26.54	3.652%	$27.5092	$27.51	$27.50	$27.50
Purchase #2	$86.31	3.695%	$89.4992	$89.50	$89.50	$89.50
Purchase #3	$245.57	4.370%	$256.3014	$256.30	$256.30	$256.30
Purchase #4	$190.29	6.147%	$201.9871	$201.99	$202.00	$202.00
Purchase #5	$221.64	5.631%	$234.1205	$234.12	$234.10	$234.10
Purchase #6	$200.68	10.835%	$222.4237	$222.42	$222.40	$222.40
Purchase #7	$32.85	6.544%	$34.9997	$35.00	$35.00	$35.00
7 purchase totals =	$1,003.88		$1,066.8408	$1,066.84	$1,066.80	$1,066.80