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	$35.47	3.860%	$36.8391	$36.84	$36.85	$36.80
Purchase #2	$226.63	11.157%	$251.9151	$251.92	$251.90	$251.90
Purchase #3	$68.59	4.208%	$71.4763	$71.48	$71.50	$71.50
Purchase #4	$112.85	9.381%	$123.4365	$123.44	$123.45	$123.40
Purchase #5	$73.65	5.328%	$77.5741	$77.57	$77.55	$77.60
Purchase #6	$84.94	5.561%	$89.6635	$89.66	$89.65	$89.70
Purchase #7	$31.34	3.516%	$32.4419	$32.44	$32.45	$32.40
7 purchase totals =	$633.47		$683.3465	$683.35	$683.35	$683.30