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	$32.90	3.136%	$33.9317	$33.93	$33.95	$33.90
Purchase #2	$160.96	12.103%	$180.441	$180.44	$180.45	$180.40
Purchase #3	$43.89	4.508%	$45.8686	$45.87	$45.85	$45.90
Purchase #4	$147.26	9.675%	$161.5074	$161.51	$161.50	$161.50
Purchase #5	$155.43	12.298%	$174.5448	$174.54	$174.55	$174.50
Purchase #6	$226.70	8.151%	$245.1783	$245.18	$245.20	$245.20
Purchase #7	$56.78	9.864%	$62.3808	$62.38	$62.40	$62.40
7 purchase totals =	$823.92		$903.8526	$903.85	$903.90	$903.80