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	$185.62	12.811%	$209.3998	$209.40	$209.40	$209.40
Purchase #2	$40.93	3.133%	$42.2123	$42.21	$42.20	$42.20
Purchase #3	$149.95	5.482%	$158.1703	$158.17	$158.15	$158.20
Purchase #4	$110.49	11.832%	$123.5632	$123.56	$123.55	$123.60
Purchase #5	$196.63	6.608%	$209.6233	$209.62	$209.60	$209.60
Purchase #6	$128.75	9.213%	$140.6117	$140.61	$140.60	$140.60
Purchase #7	$156.73	7.196%	$168.0083	$168.01	$168.00	$168.00
7 purchase totals =	$969.10		$1,051.5889	$1,051.58	$1,051.50	$1,051.60