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	$90.47	5.549%	$95.4902	$95.49	$95.50	$95.50
Purchase #2	$185.66	12.525%	$208.9139	$208.91	$208.90	$208.90
Purchase #3	$69.65	3.659%	$72.1985	$72.20	$72.20	$72.20
Purchase #4	$115.42	13.618%	$131.1379	$131.14	$131.15	$131.10
Purchase #5	$152.90	9.259%	$167.057	$167.06	$167.05	$167.10
Purchase #6	$40.75	3.825%	$42.3087	$42.31	$42.30	$42.30
Purchase #7	$99.48	13.384%	$112.7944	$112.79	$112.80	$112.80
7 purchase totals =	$754.33		$829.9006	$829.90	$829.90	$829.90