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	$111.33	8.213%	$120.4735	$120.47	$120.45	$120.50
Purchase #2	$139.79	13.674%	$158.9049	$158.90	$158.90	$158.90
Purchase #3	$207.33	8.680%	$225.3262	$225.33	$225.35	$225.30
Purchase #4	$237.40	5.141%	$249.6047	$249.60	$249.60	$249.60
Purchase #5	$79.51	11.695%	$88.8087	$88.81	$88.80	$88.80
Purchase #6	$53.89	5.331%	$56.7629	$56.76	$56.75	$56.80
Purchase #7	$64.48	4.665%	$67.488	$67.49	$67.50	$67.50
7 purchase totals =	$893.73		$967.3689	$967.36	$967.35	$967.40