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	$50.56	8.316%	$54.7646	$54.76	$54.75	$54.80
Purchase #2	$93.43	3.713%	$96.8991	$96.90	$96.90	$96.90
Purchase #3	$50.51	4.873%	$52.9714	$52.97	$52.95	$53.00
Purchase #4	$80.47	11.315%	$89.5752	$89.58	$89.60	$89.60
Purchase #5	$47.48	13.217%	$53.7554	$53.76	$53.75	$53.80
Purchase #6	$34.61	8.311%	$37.4864	$37.49	$37.50	$37.50
Purchase #7	$217.86	3.438%	$225.35	$225.35	$225.35	$225.40
7 purchase totals =	$574.92		$610.8021	$610.81	$610.80	$611.00