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	$63.40	6.165%	$67.3086	$67.31	$67.30	$67.30
Purchase #2	$188.97	3.659%	$195.8844	$195.88	$195.90	$195.90
Purchase #3	$134.42	7.359%	$144.312	$144.31	$144.30	$144.30
Purchase #4	$145.83	13.719%	$165.8364	$165.84	$165.85	$165.80
Purchase #5	$224.92	9.557%	$246.4156	$246.42	$246.40	$246.40
Purchase #6	$200.55	9.391%	$219.3837	$219.38	$219.40	$219.40
Purchase #7	$54.82	11.166%	$60.9412	$60.94	$60.95	$60.90
7 purchase totals =	$1,012.91		$1,100.0819	$1,100.08	$1,100.10	$1,100.00