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	$92.42	11.735%	$103.2655	$103.27	$103.25	$103.30
Purchase #2	$68.90	4.688%	$72.13	$72.13	$72.15	$72.10
Purchase #3	$36.35	7.786%	$39.1802	$39.18	$39.20	$39.20
Purchase #4	$31.52	3.872%	$32.7405	$32.74	$32.75	$32.70
Purchase #5	$198.73	4.674%	$208.0186	$208.02	$208.00	$208.00
Purchase #6	$207.94	5.746%	$219.8882	$219.89	$219.90	$219.90
Purchase #7	$149.64	10.136%	$164.8075	$164.81	$164.80	$164.80
7 purchase totals =	$785.50		$840.0305	$840.04	$840.05	$840.00