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	$86.59	4.336%	$90.3445	$90.34	$90.35	$90.30
Purchase #2	$201.81	5.211%	$212.3263	$212.33	$212.35	$212.30
Purchase #3	$131.79	6.656%	$140.5619	$140.56	$140.55	$140.60
Purchase #4	$100.40	4.786%	$105.2051	$105.21	$105.20	$105.20
Purchase #5	$70.81	12.588%	$79.7236	$79.72	$79.70	$79.70
Purchase #6	$173.27	6.514%	$184.5568	$184.56	$184.55	$184.60
Purchase #7	$57.33	9.328%	$62.6777	$62.68	$62.70	$62.70
7 purchase totals =	$822.00		$875.3959	$875.40	$875.40	$875.40