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	$16.26	3.240%	$16.7868	$16.79	$16.80	$16.80
Purchase #2	$86.32	3.598%	$89.4258	$89.43	$89.45	$89.40
Purchase #3	$241.51	12.222%	$271.0274	$271.03	$271.05	$271.00
Purchase #4	$124.90	5.480%	$131.7445	$131.74	$131.75	$131.70
Purchase #5	$80.85	13.584%	$91.8327	$91.83	$91.85	$91.80
Purchase #6	$37.70	6.557%	$40.172	$40.17	$40.15	$40.20
Purchase #7	$127.32	10.334%	$140.4772	$140.48	$140.50	$140.50
7 purchase totals =	$714.86		$781.4664	$781.47	$781.55	$781.40