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	$36.32	12.648%	$40.9138	$40.91	$40.90	$40.90
Purchase #2	$72.76	4.279%	$75.8734	$75.87	$75.85	$75.90
Purchase #3	$184.84	8.359%	$200.2908	$200.29	$200.30	$200.30
Purchase #4	$72.90	7.510%	$78.3748	$78.37	$78.35	$78.40
Purchase #5	$59.66	7.827%	$64.3296	$64.33	$64.35	$64.30
Purchase #6	$60.45	5.268%	$63.6345	$63.63	$63.65	$63.60
Purchase #7	$90.37	9.870%	$99.2895	$99.29	$99.30	$99.30
7 purchase totals =	$577.30		$622.7064	$622.69	$622.70	$622.70