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	$139.83	11.498%	$155.9077	$155.91	$155.90	$155.90
Purchase #2	$50.90	4.536%	$53.2088	$53.21	$53.20	$53.20
Purchase #3	$198.39	7.807%	$213.8783	$213.88	$213.90	$213.90
Purchase #4	$35.93	13.595%	$40.8147	$40.81	$40.80	$40.80
Purchase #5	$192.41	8.623%	$209.0015	$209.00	$209.00	$209.00
Purchase #6	$6.59	11.326%	$7.3364	$7.34	$7.35	$7.30
Purchase #7	$65.48	10.673%	$72.4687	$72.47	$72.45	$72.50
7 purchase totals =	$689.53		$752.6161	$752.62	$752.60	$752.60