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	$53.96	6.432%	$57.4307	$57.43	$57.45	$57.40
Purchase #2	$138.88	9.360%	$151.8792	$151.88	$151.90	$151.90
Purchase #3	$166.88	7.344%	$179.1357	$179.14	$179.15	$179.10
Purchase #4	$7.40	11.784%	$8.272	$8.27	$8.25	$8.30
Purchase #5	$189.83	5.563%	$200.3902	$200.39	$200.40	$200.40
Purchase #6	$122.54	11.674%	$136.8453	$136.85	$136.85	$136.80
Purchase #7	$161.95	12.255%	$181.797	$181.80	$181.80	$181.80
7 purchase totals =	$841.44		$915.7501	$915.76	$915.80	$915.70