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	$35.66	5.796%	$37.7269	$37.73	$37.75	$37.70
Purchase #2	$142.30	12.728%	$160.4119	$160.41	$160.40	$160.40
Purchase #3	$225.63	13.400%	$255.8644	$255.86	$255.85	$255.90
Purchase #4	$217.38	7.520%	$233.727	$233.73	$233.75	$233.70
Purchase #5	$245.58	9.584%	$269.1164	$269.12	$269.10	$269.10
Purchase #6	$180.87	8.632%	$196.4827	$196.48	$196.50	$196.50
Purchase #7	$92.92	8.155%	$100.4976	$100.50	$100.50	$100.50
7 purchase totals =	$1,140.34		$1,253.8269	$1,253.83	$1,253.85	$1,253.80