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	$206.67	6.557%	$220.2214	$220.22	$220.20	$220.20
Purchase #2	$241.88	4.137%	$251.8866	$251.89	$251.90	$251.90
Purchase #3	$26.27	9.225%	$28.6934	$28.69	$28.70	$28.70
Purchase #4	$93.28	13.438%	$105.815	$105.82	$105.80	$105.80
Purchase #5	$186.56	12.313%	$209.5311	$209.53	$209.55	$209.50
Purchase #6	$131.93	3.743%	$136.8681	$136.87	$136.85	$136.90
Purchase #7	$78.54	6.760%	$83.8493	$83.85	$83.85	$83.80
7 purchase totals =	$965.13		$1,036.8649	$1,036.87	$1,036.85	$1,036.80