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	$50.36	11.692%	$56.2481	$56.25	$56.25	$56.20
Purchase #2	$178.96	7.242%	$191.9203	$191.92	$191.90	$191.90
Purchase #3	$152.93	12.116%	$171.459	$171.46	$171.45	$171.50
Purchase #4	$31.38	12.795%	$35.3951	$35.40	$35.40	$35.40
Purchase #5	$52.81	8.212%	$57.1468	$57.15	$57.15	$57.10
Purchase #6	$164.30	5.675%	$173.624	$173.62	$173.60	$173.60
Purchase #7	$239.52	10.511%	$264.6959	$264.70	$264.70	$264.70
7 purchase totals =	$870.26		$950.4892	$950.50	$950.45	$950.40