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	$101.28	3.811%	$105.1398	$105.14	$105.15	$105.10
Purchase #2	$96.94	3.686%	$100.5132	$100.51	$100.50	$100.50
Purchase #3	$26.46	12.798%	$29.8464	$29.85	$29.85	$29.80
Purchase #4	$181.43	11.244%	$201.83	$201.83	$201.85	$201.80
Purchase #5	$155.84	11.573%	$173.8754	$173.88	$173.90	$173.90
Purchase #6	$59.97	12.656%	$67.5598	$67.56	$67.55	$67.60
Purchase #7	$79.50	12.366%	$89.331	$89.33	$89.35	$89.30
7 purchase totals =	$701.42		$768.0956	$768.10	$768.15	$768.00