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	$123.35	10.438%	$136.2253	$136.23	$136.25	$136.20
Purchase #2	$77.34	8.340%	$83.7902	$83.79	$83.80	$83.80
Purchase #3	$197.65	7.423%	$212.3216	$212.32	$212.30	$212.30
Purchase #4	$9.71	7.705%	$10.4582	$10.46	$10.45	$10.50
Purchase #5	$39.90	10.749%	$44.1889	$44.19	$44.20	$44.20
Purchase #6	$22.40	11.826%	$25.049	$25.05	$25.05	$25.00
Purchase #7	$55.83	6.705%	$59.5734	$59.57	$59.55	$59.60
7 purchase totals =	$526.18		$571.6066	$571.61	$571.60	$571.60