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	$239.30	13.161%	$270.7943	$270.79	$270.80	$270.80
Purchase #2	$171.56	6.240%	$182.2653	$182.27	$182.25	$182.30
Purchase #3	$204.50	6.571%	$217.9377	$217.94	$217.95	$217.90
Purchase #4	$12.94	5.107%	$13.6008	$13.60	$13.60	$13.60
Purchase #5	$82.41	4.399%	$86.0352	$86.04	$86.05	$86.00
Purchase #6	$179.89	10.700%	$199.1382	$199.14	$199.15	$199.10
Purchase #7	$32.47	10.555%	$35.8972	$35.90	$35.90	$35.90
7 purchase totals =	$923.07		$1,005.6687	$1,005.68	$1,005.70	$1,005.60