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	$60.61	8.215%	$65.5891	$65.59	$65.60	$65.60
Purchase #2	$236.76	11.680%	$264.4136	$264.41	$264.40	$264.40
Purchase #3	$198.83	5.423%	$209.6126	$209.61	$209.60	$209.60
Purchase #4	$83.38	3.547%	$86.3375	$86.34	$86.35	$86.30
Purchase #5	$170.35	9.276%	$186.1517	$186.15	$186.15	$186.20
Purchase #6	$171.31	7.811%	$184.691	$184.69	$184.70	$184.70
Purchase #7	$147.64	8.379%	$160.0108	$160.01	$160.00	$160.00
7 purchase totals =	$1,068.88		$1,156.8063	$1,156.80	$1,156.80	$1,156.80