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	$115.71	7.199%	$124.04	$124.04	$124.05	$124.00
Purchase #2	$80.65	10.401%	$89.0384	$89.04	$89.05	$89.00
Purchase #3	$166.89	3.557%	$172.8263	$172.83	$172.85	$172.80
Purchase #4	$215.46	4.625%	$225.425	$225.43	$225.45	$225.40
Purchase #5	$22.46	9.303%	$24.5495	$24.55	$24.55	$24.50
Purchase #6	$104.91	7.284%	$112.5516	$112.55	$112.55	$112.60
Purchase #7	$210.79	13.170%	$238.551	$238.55	$238.55	$238.60
7 purchase totals =	$916.87		$986.9818	$986.99	$987.05	$986.90