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	$179.83	3.215%	$185.6115	$185.61	$185.60	$185.60
Purchase #2	$104.72	7.465%	$112.5373	$112.54	$112.55	$112.50
Purchase #3	$198.37	5.793%	$209.8616	$209.86	$209.85	$209.90
Purchase #4	$65.29	3.772%	$67.7527	$67.75	$67.75	$67.80
Purchase #5	$125.55	10.279%	$138.4553	$138.46	$138.45	$138.50
Purchase #6	$107.47	5.109%	$112.9606	$112.96	$112.95	$113.00
Purchase #7	$244.56	7.472%	$262.8335	$262.83	$262.85	$262.80
7 purchase totals =	$1,025.79		$1,090.0125	$1,090.01	$1,090.00	$1,090.10