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	$38.72	8.571%	$42.0387	$42.04	$42.05	$42.00
Purchase #2	$233.97	8.302%	$253.3942	$253.39	$253.40	$253.40
Purchase #3	$217.41	9.155%	$237.3139	$237.31	$237.30	$237.30
Purchase #4	$166.85	9.741%	$183.1029	$183.10	$183.10	$183.10
Purchase #5	$21.84	4.827%	$22.8942	$22.89	$22.90	$22.90
Purchase #6	$136.83	4.295%	$142.7068	$142.71	$142.70	$142.70
Purchase #7	$210.73	5.401%	$222.1115	$222.11	$222.10	$222.10
7 purchase totals =	$1,026.35		$1,103.5622	$1,103.55	$1,103.55	$1,103.50