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	$138.93	12.669%	$156.531	$156.53	$156.55	$156.50
Purchase #2	$86.58	3.817%	$89.8848	$89.88	$89.90	$89.90
Purchase #3	$227.87	4.388%	$237.8689	$237.87	$237.85	$237.90
Purchase #4	$131.70	9.570%	$144.3037	$144.30	$144.30	$144.30
Purchase #5	$170.53	5.758%	$180.3491	$180.35	$180.35	$180.30
Purchase #6	$245.48	6.186%	$260.6654	$260.67	$260.65	$260.70
Purchase #7	$78.69	5.656%	$83.1407	$83.14	$83.15	$83.10
7 purchase totals =	$1,079.78		$1,152.7436	$1,152.74	$1,152.75	$1,152.70