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	$86.78	7.292%	$93.108	$93.11	$93.10	$93.10
Purchase #2	$122.27	4.271%	$127.4922	$127.49	$127.50	$127.50
Purchase #3	$237.77	4.558%	$248.6076	$248.61	$248.60	$248.60
Purchase #4	$71.90	9.811%	$78.9541	$78.95	$78.95	$79.00
Purchase #5	$236.40	3.676%	$245.0901	$245.09	$245.10	$245.10
Purchase #6	$96.86	8.536%	$105.128	$105.13	$105.15	$105.10
Purchase #7	$75.84	9.294%	$82.8886	$82.89	$82.90	$82.90
7 purchase totals =	$927.82		$981.2686	$981.27	$981.30	$981.30