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	$52.92	13.174%	$59.8917	$59.89	$59.90	$59.90
Purchase #2	$131.69	7.625%	$141.7314	$141.73	$141.75	$141.70
Purchase #3	$210.31	8.666%	$228.5355	$228.54	$228.55	$228.50
Purchase #4	$202.51	7.293%	$217.2791	$217.28	$217.30	$217.30
Purchase #5	$62.82	6.704%	$67.0315	$67.03	$67.05	$67.00
Purchase #6	$99.28	8.662%	$107.8796	$107.88	$107.90	$107.90
Purchase #7	$39.97	12.668%	$45.0334	$45.03	$45.05	$45.00
7 purchase totals =	$799.50		$867.3822	$867.38	$867.50	$867.30