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	$211.78	3.471%	$219.1309	$219.13	$219.15	$219.10
Purchase #2	$193.86	12.855%	$218.7807	$218.78	$218.80	$218.80
Purchase #3	$121.55	13.193%	$137.5861	$137.59	$137.60	$137.60
Purchase #4	$100.90	9.330%	$110.314	$110.31	$110.30	$110.30
Purchase #5	$37.37	9.272%	$40.8349	$40.83	$40.85	$40.80
Purchase #6	$92.89	12.782%	$104.7632	$104.76	$104.75	$104.80
Purchase #7	$79.66	12.714%	$89.788	$89.79	$89.80	$89.80
7 purchase totals =	$838.01		$921.1978	$921.19	$921.25	$921.20