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	$104.79	11.859%	$117.217	$117.22	$117.20	$117.20
Purchase #2	$156.25	3.313%	$161.4266	$161.43	$161.45	$161.40
Purchase #3	$50.31	6.452%	$53.556	$53.56	$53.55	$53.60
Purchase #4	$53.30	11.834%	$59.6075	$59.61	$59.60	$59.60
Purchase #5	$28.43	11.833%	$31.7941	$31.79	$31.80	$31.80
Purchase #6	$189.85	10.165%	$209.1483	$209.15	$209.15	$209.10
Purchase #7	$240.78	8.177%	$260.4686	$260.47	$260.45	$260.50
7 purchase totals =	$823.71		$893.2181	$893.23	$893.20	$893.20