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	$87.66	4.811%	$91.8773	$91.88	$91.90	$91.90
Purchase #2	$114.35	5.221%	$120.3202	$120.32	$120.30	$120.30
Purchase #3	$47.70	4.116%	$49.6633	$49.66	$49.65	$49.70
Purchase #4	$39.40	10.570%	$43.5646	$43.56	$43.55	$43.60
Purchase #5	$19.28	8.725%	$20.9622	$20.96	$20.95	$21.00
Purchase #6	$186.51	5.489%	$196.7475	$196.75	$196.75	$196.70
Purchase #7	$46.69	10.372%	$51.5327	$51.53	$51.55	$51.50
7 purchase totals =	$541.59		$574.6678	$574.66	$574.65	$574.70