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	$44.83	3.745%	$46.5089	$46.51	$46.50	$46.50
Purchase #2	$148.82	13.206%	$168.4732	$168.47	$168.45	$168.50
Purchase #3	$190.73	8.289%	$206.5396	$206.54	$206.55	$206.50
Purchase #4	$141.38	5.761%	$149.5249	$149.52	$149.50	$149.50
Purchase #5	$147.85	8.116%	$159.8495	$159.85	$159.85	$159.80
Purchase #6	$62.39	10.254%	$68.7875	$68.79	$68.80	$68.80
Purchase #7	$164.85	8.578%	$178.9908	$178.99	$179.00	$179.00
7 purchase totals =	$900.85		$978.6744	$978.67	$978.65	$978.60