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	$198.74	10.123%	$218.8585	$218.86	$218.85	$218.90
Purchase #2	$115.65	4.376%	$120.7108	$120.71	$120.70	$120.70
Purchase #3	$157.64	9.400%	$172.4582	$172.46	$172.45	$172.50
Purchase #4	$219.59	8.809%	$238.9337	$238.93	$238.95	$238.90
Purchase #5	$232.69	9.771%	$255.4261	$255.43	$255.45	$255.40
Purchase #6	$29.94	5.301%	$31.5271	$31.53	$31.55	$31.50
Purchase #7	$218.44	9.356%	$238.8772	$238.88	$238.90	$238.90
7 purchase totals =	$1,172.69		$1,276.7916	$1,276.80	$1,276.85	$1,276.80