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	$250.82	12.238%	$281.5154	$281.52	$281.50	$281.50
Purchase #2	$201.77	3.760%	$209.3566	$209.36	$209.35	$209.40
Purchase #3	$67.31	6.712%	$71.8278	$71.83	$71.85	$71.80
Purchase #4	$93.75	7.114%	$100.4194	$100.42	$100.40	$100.40
Purchase #5	$188.64	3.140%	$194.5633	$194.56	$194.55	$194.60
Purchase #6	$36.64	4.619%	$38.3324	$38.33	$38.35	$38.30
Purchase #7	$5.77	11.506%	$6.4339	$6.43	$6.45	$6.40
7 purchase totals =	$844.70		$902.4488	$902.45	$902.45	$902.40