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	$67.57	6.678%	$72.0823	$72.08	$72.10	$72.10
Purchase #2	$114.86	7.659%	$123.6571	$123.66	$123.65	$123.70
Purchase #3	$36.61	10.348%	$40.3984	$40.40	$40.40	$40.40
Purchase #4	$67.66	3.676%	$70.1472	$70.15	$70.15	$70.10
Purchase #5	$11.43	12.188%	$12.8231	$12.82	$12.80	$12.80
Purchase #6	$125.98	11.659%	$140.668	$140.67	$140.65	$140.70
Purchase #7	$188.39	13.274%	$213.3969	$213.40	$213.40	$213.40
7 purchase totals =	$612.50		$673.1730	$673.18	$673.15	$673.20