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	$174.61	6.680%	$186.2739	$186.27	$186.25	$186.30
Purchase #2	$97.55	8.416%	$105.7598	$105.76	$105.75	$105.80
Purchase #3	$129.41	13.446%	$146.8105	$146.81	$146.80	$146.80
Purchase #4	$36.61	8.678%	$39.787	$39.79	$39.80	$39.80
Purchase #5	$98.83	5.478%	$104.2439	$104.24	$104.25	$104.20
Purchase #6	$90.99	9.786%	$99.8943	$99.89	$99.90	$99.90
Purchase #7	$175.32	8.307%	$189.8838	$189.88	$189.90	$189.90
7 purchase totals =	$803.32		$872.6532	$872.64	$872.65	$872.70