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	$156.49	5.298%	$164.7808	$164.78	$164.80	$164.80
Purchase #2	$218.31	13.464%	$247.7033	$247.70	$247.70	$247.70
Purchase #3	$147.57	4.684%	$154.4822	$154.48	$154.50	$154.50
Purchase #4	$68.64	3.285%	$70.8948	$70.89	$70.90	$70.90
Purchase #5	$93.36	11.314%	$103.9228	$103.92	$103.90	$103.90
Purchase #6	$66.79	6.222%	$70.9457	$70.95	$70.95	$70.90
Purchase #7	$52.63	11.824%	$58.853	$58.85	$58.85	$58.90
7 purchase totals =	$803.79		$871.5826	$871.57	$871.60	$871.60