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	$236.89	5.706%	$250.4069	$250.41	$250.40	$250.40
Purchase #2	$210.61	9.618%	$230.8665	$230.87	$230.85	$230.90
Purchase #3	$40.73	5.212%	$42.8528	$42.85	$42.85	$42.90
Purchase #4	$110.75	13.292%	$125.4709	$125.47	$125.45	$125.50
Purchase #5	$123.44	10.318%	$136.1765	$136.18	$136.20	$136.20
Purchase #6	$93.75	8.333%	$101.5622	$101.56	$101.55	$101.60
Purchase #7	$119.38	3.718%	$123.8185	$123.82	$123.80	$123.80
7 purchase totals =	$935.55		$1,011.1543	$1,011.16	$1,011.10	$1,011.30