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	$136.54	13.863%	$155.4685	$155.47	$155.45	$155.50
Purchase #2	$216.69	3.197%	$223.6176	$223.62	$223.60	$223.60
Purchase #3	$158.46	6.541%	$168.8249	$168.82	$168.80	$168.80
Purchase #4	$68.40	3.103%	$70.5225	$70.52	$70.50	$70.50
Purchase #5	$165.70	3.220%	$171.0355	$171.04	$171.05	$171.00
Purchase #6	$136.49	3.181%	$140.8317	$140.83	$140.85	$140.80
Purchase #7	$25.58	8.662%	$27.7957	$27.80	$27.80	$27.80
7 purchase totals =	$907.86		$958.0964	$958.10	$958.05	$958.00