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	$74.45	11.539%	$83.0408	$83.04	$83.05	$83.00
Purchase #2	$10.94	6.372%	$11.6371	$11.64	$11.65	$11.60
Purchase #3	$154.38	6.542%	$164.4795	$164.48	$164.50	$164.50
Purchase #4	$103.33	11.188%	$114.8906	$114.89	$114.90	$114.90
Purchase #5	$76.69	13.306%	$86.8944	$86.89	$86.90	$86.90
Purchase #6	$236.74	5.775%	$250.4117	$250.41	$250.40	$250.40
Purchase #7	$171.62	9.205%	$187.4176	$187.42	$187.40	$187.40
7 purchase totals =	$828.15		$898.7717	$898.77	$898.80	$898.70