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	$75.43	13.442%	$85.5693	$85.57	$85.55	$85.60
Purchase #2	$64.75	4.463%	$67.6398	$67.64	$67.65	$67.60
Purchase #3	$129.96	9.752%	$142.6337	$142.63	$142.65	$142.60
Purchase #4	$53.95	9.523%	$59.0877	$59.09	$59.10	$59.10
Purchase #5	$166.90	9.873%	$183.378	$183.38	$183.40	$183.40
Purchase #6	$18.73	8.448%	$20.3123	$20.31	$20.30	$20.30
Purchase #7	$84.88	7.610%	$91.3394	$91.34	$91.35	$91.30
7 purchase totals =	$594.60		$649.9602	$649.96	$650.00	$649.90