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	$41.30	3.415%	$42.7104	$42.71	$42.70	$42.70
Purchase #2	$243.80	12.227%	$273.6094	$273.61	$273.60	$273.60
Purchase #3	$92.27	13.215%	$104.4635	$104.46	$104.45	$104.50
Purchase #4	$48.75	8.115%	$52.7061	$52.71	$52.70	$52.70
Purchase #5	$54.29	7.796%	$58.5224	$58.52	$58.50	$58.50
Purchase #6	$75.66	3.270%	$78.1341	$78.13	$78.15	$78.10
Purchase #7	$125.89	9.533%	$137.8911	$137.89	$137.90	$137.90
7 purchase totals =	$681.96		$748.0370	$748.03	$748.00	$748.00