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	$81.91	9.190%	$89.4375	$89.44	$89.45	$89.40
Purchase #2	$88.61	8.430%	$96.0798	$96.08	$96.10	$96.10
Purchase #3	$19.68	6.756%	$21.0096	$21.01	$21.00	$21.00
Purchase #4	$230.86	11.216%	$256.7533	$256.75	$256.75	$256.80
Purchase #5	$25.38	10.186%	$27.9652	$27.97	$27.95	$28.00
Purchase #6	$174.36	12.681%	$196.4706	$196.47	$196.45	$196.50
Purchase #7	$164.90	8.231%	$178.4729	$178.47	$178.45	$178.50
7 purchase totals =	$785.70		$866.1889	$866.19	$866.15	$866.30