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	$40.33	6.180%	$42.8224	$42.82	$42.80	$42.80
Purchase #2	$233.44	13.359%	$264.6252	$264.63	$264.65	$264.60
Purchase #3	$232.83	6.318%	$247.5402	$247.54	$247.55	$247.50
Purchase #4	$29.76	7.582%	$32.0164	$32.02	$32.00	$32.00
Purchase #5	$175.79	12.367%	$197.5299	$197.53	$197.55	$197.50
Purchase #6	$79.83	8.736%	$86.8039	$86.80	$86.80	$86.80
Purchase #7	$123.34	10.649%	$136.4745	$136.47	$136.45	$136.50
7 purchase totals =	$915.32		$1,007.8125	$1,007.81	$1,007.80	$1,007.70