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	$210.89	12.417%	$237.0762	$237.08	$237.10	$237.10
Purchase #2	$66.84	4.824%	$70.0644	$70.06	$70.05	$70.10
Purchase #3	$80.40	12.586%	$90.5191	$90.52	$90.50	$90.50
Purchase #4	$138.52	4.367%	$144.5692	$144.57	$144.55	$144.60
Purchase #5	$149.69	9.828%	$164.4015	$164.40	$164.40	$164.40
Purchase #6	$67.57	6.211%	$71.7668	$71.77	$71.75	$71.80
Purchase #7	$236.90	10.527%	$261.8385	$261.84	$261.85	$261.80
7 purchase totals =	$950.81		$1,040.2357	$1,040.24	$1,040.20	$1,040.30