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	$53.48	6.333%	$56.8669	$56.87	$56.85	$56.90
Purchase #2	$182.32	7.600%	$196.1763	$196.18	$196.20	$196.20
Purchase #3	$155.87	5.238%	$164.0345	$164.03	$164.05	$164.00
Purchase #4	$63.98	8.601%	$69.4829	$69.48	$69.50	$69.50
Purchase #5	$138.37	13.676%	$157.2935	$157.29	$157.30	$157.30
Purchase #6	$62.96	13.241%	$71.2965	$71.30	$71.30	$71.30
Purchase #7	$29.98	9.207%	$32.7403	$32.74	$32.75	$32.70
7 purchase totals =	$686.96		$747.8909	$747.89	$747.95	$747.90