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	$22.90	9.505%	$25.0766	$25.08	$25.10	$25.10
Purchase #2	$87.91	3.219%	$90.7398	$90.74	$90.75	$90.70
Purchase #3	$77.63	5.729%	$82.0774	$82.08	$82.10	$82.10
Purchase #4	$63.81	11.236%	$70.9797	$70.98	$71.00	$71.00
Purchase #5	$136.32	7.334%	$146.3177	$146.32	$146.30	$146.30
Purchase #6	$196.36	6.291%	$208.713	$208.71	$208.70	$208.70
Purchase #7	$184.65	8.710%	$200.733	$200.73	$200.75	$200.70
7 purchase totals =	$769.58		$824.6372	$824.64	$824.70	$824.60