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	$30.98	9.400%	$33.8921	$33.89	$33.90	$33.90
Purchase #2	$92.69	12.750%	$104.508	$104.51	$104.50	$104.50
Purchase #3	$122.88	13.480%	$139.4442	$139.44	$139.45	$139.40
Purchase #4	$120.90	8.627%	$131.33	$131.33	$131.35	$131.30
Purchase #5	$219.81	11.856%	$245.8707	$245.87	$245.85	$245.90
Purchase #6	$123.65	12.751%	$139.4166	$139.42	$139.40	$139.40
Purchase #7	$114.53	13.581%	$130.0843	$130.08	$130.10	$130.10
7 purchase totals =	$825.44		$924.5459	$924.54	$924.55	$924.50