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	$94.46	3.460%	$97.7283	$97.73	$97.75	$97.70
Purchase #2	$120.83	5.537%	$127.5204	$127.52	$127.50	$127.50
Purchase #3	$109.52	3.131%	$112.9491	$112.95	$112.95	$112.90
Purchase #4	$176.88	5.140%	$185.9716	$185.97	$185.95	$186.00
Purchase #5	$243.27	6.477%	$259.0266	$259.03	$259.05	$259.00
Purchase #6	$26.38	3.327%	$27.2577	$27.26	$27.25	$27.30
Purchase #7	$171.80	10.817%	$190.3836	$190.38	$190.40	$190.40
7 purchase totals =	$943.14		$1,000.8373	$1,000.84	$1,000.85	$1,000.80