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	$108.25	5.657%	$114.3737	$114.37	$114.35	$114.40
Purchase #2	$150.88	10.801%	$167.1765	$167.18	$167.20	$167.20
Purchase #3	$118.77	6.525%	$126.5197	$126.52	$126.50	$126.50
Purchase #4	$152.50	10.292%	$168.1953	$168.20	$168.20	$168.20
Purchase #5	$25.94	12.266%	$29.1218	$29.12	$29.10	$29.10
Purchase #6	$76.53	3.142%	$78.9346	$78.93	$78.95	$78.90
Purchase #7	$140.66	3.839%	$146.0599	$146.06	$146.05	$146.10
7 purchase totals =	$773.53		$830.3815	$830.38	$830.35	$830.40