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	$22.77	12.628%	$25.6454	$25.65	$25.65	$25.60
Purchase #2	$84.74	5.390%	$89.3075	$89.31	$89.30	$89.30
Purchase #3	$168.89	13.664%	$191.9671	$191.97	$191.95	$192.00
Purchase #4	$59.50	7.382%	$63.8923	$63.89	$63.90	$63.90
Purchase #5	$237.61	11.174%	$264.1605	$264.16	$264.15	$264.20
Purchase #6	$78.89	11.560%	$88.0097	$88.01	$88.00	$88.00
Purchase #7	$56.83	9.660%	$62.3198	$62.32	$62.30	$62.30
7 purchase totals =	$709.23		$785.3023	$785.31	$785.25	$785.30