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	$73.73	11.805%	$82.4338	$82.43	$82.45	$82.40
Purchase #2	$76.88	8.787%	$83.6354	$83.64	$83.65	$83.60
Purchase #3	$139.32	6.469%	$148.3326	$148.33	$148.35	$148.30
Purchase #4	$36.30	6.867%	$38.7927	$38.79	$38.80	$38.80
Purchase #5	$45.52	12.337%	$51.1358	$51.14	$51.15	$51.10
Purchase #6	$118.39	4.283%	$123.4606	$123.46	$123.45	$123.50
Purchase #7	$124.34	7.404%	$133.5461	$133.55	$133.55	$133.50
7 purchase totals =	$614.48		$661.3370	$661.34	$661.40	$661.20