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	$115.31	13.353%	$130.7073	$130.71	$130.70	$130.70
Purchase #2	$67.50	3.592%	$69.9246	$69.92	$69.90	$69.90
Purchase #3	$188.33	11.756%	$210.4701	$210.47	$210.45	$210.50
Purchase #4	$184.78	12.822%	$208.4725	$208.47	$208.45	$208.50
Purchase #5	$116.39	4.693%	$121.8522	$121.85	$121.85	$121.90
Purchase #6	$89.82	9.616%	$98.4571	$98.46	$98.45	$98.50
Purchase #7	$78.34	9.690%	$85.9311	$85.93	$85.95	$85.90
7 purchase totals =	$840.47		$925.8149	$925.81	$925.75	$925.90