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	$78.56	6.766%	$83.8754	$83.88	$83.90	$83.90
Purchase #2	$45.58	7.271%	$48.8941	$48.89	$48.90	$48.90
Purchase #3	$84.61	12.378%	$95.083	$95.08	$95.10	$95.10
Purchase #4	$62.51	3.794%	$64.8816	$64.88	$64.90	$64.90
Purchase #5	$230.50	8.185%	$249.3664	$249.37	$249.35	$249.40
Purchase #6	$243.38	4.719%	$254.8651	$254.87	$254.85	$254.90
Purchase #7	$91.85	8.773%	$99.908	$99.91	$99.90	$99.90
7 purchase totals =	$836.99		$896.8736	$896.88	$896.90	$897.00