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	$77.25	8.619%	$83.9082	$83.91	$83.90	$83.90
Purchase #2	$18.60	10.540%	$20.5604	$20.56	$20.55	$20.60
Purchase #3	$215.49	3.556%	$223.1528	$223.15	$223.15	$223.20
Purchase #4	$5.54	5.473%	$5.8432	$5.84	$5.85	$5.80
Purchase #5	$86.88	3.109%	$89.5811	$89.58	$89.60	$89.60
Purchase #6	$149.74	12.258%	$168.0951	$168.10	$168.10	$168.10
Purchase #7	$166.56	13.832%	$189.5986	$189.60	$189.60	$189.60
7 purchase totals =	$720.06		$780.7394	$780.74	$780.75	$780.80