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	$186.43	10.823%	$206.6073	$206.61	$206.60	$206.60
Purchase #2	$171.65	8.271%	$185.8472	$185.85	$185.85	$185.80
Purchase #3	$83.25	12.780%	$93.8894	$93.89	$93.90	$93.90
Purchase #4	$108.34	10.130%	$119.3148	$119.31	$119.30	$119.30
Purchase #5	$65.29	5.134%	$68.642	$68.64	$68.65	$68.60
Purchase #6	$56.38	7.542%	$60.6322	$60.63	$60.65	$60.60
Purchase #7	$169.45	12.474%	$190.5872	$190.59	$190.60	$190.60
7 purchase totals =	$840.79		$925.5201	$925.52	$925.55	$925.40