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	$65.32	3.322%	$67.4899	$67.49	$67.50	$67.50
Purchase #2	$106.48	4.835%	$111.6283	$111.63	$111.65	$111.60
Purchase #3	$159.44	11.787%	$178.2332	$178.23	$178.25	$178.20
Purchase #4	$233.30	11.243%	$259.5299	$259.53	$259.55	$259.50
Purchase #5	$42.44	4.796%	$44.4754	$44.48	$44.50	$44.50
Purchase #6	$168.69	7.764%	$181.7871	$181.79	$181.80	$181.80
Purchase #7	$137.73	7.866%	$148.5638	$148.56	$148.55	$148.60
7 purchase totals =	$913.40		$991.7076	$991.71	$991.80	$991.70