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	$95.61	9.616%	$104.8039	$104.80	$104.80	$104.80
Purchase #2	$162.35	10.580%	$179.5266	$179.53	$179.55	$179.50
Purchase #3	$132.34	5.874%	$140.1137	$140.11	$140.10	$140.10
Purchase #4	$35.53	6.559%	$37.8604	$37.86	$37.85	$37.90
Purchase #5	$227.27	5.129%	$238.9267	$238.93	$238.95	$238.90
Purchase #6	$24.30	4.653%	$25.4307	$25.43	$25.45	$25.40
Purchase #7	$188.39	11.427%	$209.9173	$209.92	$209.90	$209.90
7 purchase totals =	$865.79		$936.5793	$936.58	$936.60	$936.50