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	$104.73	6.650%	$111.6945	$111.69	$111.70	$111.70
Purchase #2	$139.31	8.107%	$150.6039	$150.60	$150.60	$150.60
Purchase #3	$223.96	13.740%	$254.7321	$254.73	$254.75	$254.70
Purchase #4	$39.40	3.173%	$40.6502	$40.65	$40.65	$40.70
Purchase #5	$200.27	4.228%	$208.7374	$208.74	$208.75	$208.70
Purchase #6	$21.55	11.179%	$23.9591	$23.96	$23.95	$24.00
Purchase #7	$58.70	4.376%	$61.2687	$61.27	$61.25	$61.30
7 purchase totals =	$787.92		$851.6459	$851.64	$851.65	$851.70