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	$37.76	12.622%	$42.5261	$42.53	$42.55	$42.50
Purchase #2	$126.93	11.557%	$141.5993	$141.60	$141.60	$141.60
Purchase #3	$9.96	8.495%	$10.8061	$10.81	$10.80	$10.80
Purchase #4	$250.61	12.865%	$282.851	$282.85	$282.85	$282.90
Purchase #5	$19.80	10.567%	$21.8923	$21.89	$21.90	$21.90
Purchase #6	$86.76	4.334%	$90.5202	$90.52	$90.50	$90.50
Purchase #7	$211.47	10.813%	$234.3363	$234.34	$234.35	$234.30
7 purchase totals =	$743.29		$824.5313	$824.54	$824.55	$824.50