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	$130.85	4.608%	$136.8796	$136.88	$136.90	$136.90
Purchase #2	$71.45	9.702%	$78.3821	$78.38	$78.40	$78.40
Purchase #3	$208.90	13.695%	$237.5089	$237.51	$237.50	$237.50
Purchase #4	$229.96	8.647%	$249.8446	$249.84	$249.85	$249.80
Purchase #5	$200.77	8.439%	$217.713	$217.71	$217.70	$217.70
Purchase #6	$6.83	13.229%	$7.7335	$7.73	$7.75	$7.70
Purchase #7	$203.51	7.708%	$219.1966	$219.20	$219.20	$219.20
7 purchase totals =	$1,052.27		$1,147.2583	$1,147.25	$1,147.30	$1,147.20