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	$131.39	3.140%	$135.5156	$135.52	$135.50	$135.50
Purchase #2	$87.77	5.360%	$92.4745	$92.47	$92.45	$92.50
Purchase #3	$164.75	12.661%	$185.609	$185.61	$185.60	$185.60
Purchase #4	$247.87	11.172%	$275.562	$275.56	$275.55	$275.60
Purchase #5	$50.28	11.489%	$56.0567	$56.06	$56.05	$56.10
Purchase #6	$209.36	13.498%	$237.6194	$237.62	$237.60	$237.60
Purchase #7	$43.39	12.669%	$48.8871	$48.89	$48.90	$48.90
7 purchase totals =	$934.81		$1,031.7243	$1,031.73	$1,031.65	$1,031.80