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	$121.51	10.168%	$133.8651	$133.87	$133.85	$133.90
Purchase #2	$176.79	11.185%	$196.564	$196.56	$196.55	$196.60
Purchase #3	$206.77	13.299%	$234.2683	$234.27	$234.25	$234.30
Purchase #4	$75.92	5.587%	$80.1617	$80.16	$80.15	$80.20
Purchase #5	$178.37	5.681%	$188.5032	$188.50	$188.50	$188.50
Purchase #6	$18.81	11.187%	$20.9143	$20.91	$20.90	$20.90
Purchase #7	$240.54	13.717%	$273.5349	$273.53	$273.55	$273.50
7 purchase totals =	$1,018.71		$1,127.8115	$1,127.80	$1,127.75	$1,127.90