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	$85.73	4.115%	$89.2578	$89.26	$89.25	$89.30
Purchase #2	$111.62	9.551%	$122.2808	$122.28	$122.30	$122.30
Purchase #3	$151.50	3.484%	$156.7783	$156.78	$156.80	$156.80
Purchase #4	$187.32	7.343%	$201.0749	$201.07	$201.05	$201.10
Purchase #5	$85.85	4.141%	$89.405	$89.41	$89.40	$89.40
Purchase #6	$92.35	10.275%	$101.839	$101.84	$101.85	$101.80
Purchase #7	$59.56	12.309%	$66.8912	$66.89	$66.90	$66.90
7 purchase totals =	$773.93		$827.5270	$827.53	$827.55	$827.60