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	$168.39	3.468%	$174.2298	$174.23	$174.25	$174.20
Purchase #2	$128.59	5.852%	$136.1151	$136.12	$136.10	$136.10
Purchase #3	$38.50	10.506%	$42.5448	$42.54	$42.55	$42.50
Purchase #4	$85.68	4.863%	$89.8466	$89.85	$89.85	$89.80
Purchase #5	$67.44	5.340%	$71.0413	$71.04	$71.05	$71.00
Purchase #6	$124.90	7.601%	$134.3936	$134.39	$134.40	$134.40
Purchase #7	$166.50	4.315%	$173.6845	$173.68	$173.70	$173.70
7 purchase totals =	$780.00		$821.8557	$821.85	$821.90	$821.70