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	$246.48	7.150%	$264.1033	$264.10	$264.10	$264.10
Purchase #2	$138.94	11.497%	$154.9139	$154.91	$154.90	$154.90
Purchase #3	$208.84	8.169%	$225.9001	$225.90	$225.90	$225.90
Purchase #4	$67.44	6.658%	$71.9302	$71.93	$71.95	$71.90
Purchase #5	$122.70	4.192%	$127.8436	$127.84	$127.85	$127.80
Purchase #6	$156.31	5.870%	$165.4854	$165.49	$165.50	$165.50
Purchase #7	$69.93	12.696%	$78.8083	$78.81	$78.80	$78.80
7 purchase totals =	$1,010.64		$1,088.9848	$1,088.98	$1,089.00	$1,088.90