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	$96.67	7.460%	$103.8816	$103.88	$103.90	$103.90
Purchase #2	$203.73	3.210%	$210.2697	$210.27	$210.25	$210.30
Purchase #3	$116.86	9.800%	$128.3123	$128.31	$128.30	$128.30
Purchase #4	$97.37	10.206%	$107.3076	$107.31	$107.30	$107.30
Purchase #5	$64.71	6.547%	$68.9466	$68.95	$68.95	$68.90
Purchase #6	$86.26	4.218%	$89.8984	$89.90	$89.90	$89.90
Purchase #7	$57.37	5.453%	$60.4984	$60.50	$60.50	$60.50
7 purchase totals =	$722.97		$769.1146	$769.12	$769.10	$769.10