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	$17.69	8.274%	$19.1537	$19.15	$19.15	$19.20
Purchase #2	$117.73	6.467%	$125.3436	$125.34	$125.35	$125.30
Purchase #3	$74.67	11.603%	$83.334	$83.33	$83.35	$83.30
Purchase #4	$7.46	5.650%	$7.8815	$7.88	$7.90	$7.90
Purchase #5	$7.89	4.817%	$8.2701	$8.27	$8.25	$8.30
Purchase #6	$22.78	13.384%	$25.8289	$25.83	$25.85	$25.80
Purchase #7	$127.28	9.584%	$139.4785	$139.48	$139.50	$139.50
7 purchase totals =	$375.50		$409.2903	$409.28	$409.35	$409.30