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	$183.64	3.482%	$190.0343	$190.03	$190.05	$190.00
Purchase #2	$202.46	7.680%	$218.0089	$218.01	$218.00	$218.00
Purchase #3	$17.96	11.684%	$20.0584	$20.06	$20.05	$20.10
Purchase #4	$168.89	12.834%	$190.5653	$190.57	$190.55	$190.60
Purchase #5	$48.35	13.272%	$54.767	$54.77	$54.75	$54.80
Purchase #6	$104.66	8.465%	$113.5195	$113.52	$113.50	$113.50
Purchase #7	$35.28	7.414%	$37.8957	$37.90	$37.90	$37.90
7 purchase totals =	$761.24		$824.8491	$824.86	$824.80	$824.90