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	$38.36	5.279%	$40.385	$40.39	$40.40	$40.40
Purchase #2	$245.80	11.158%	$273.2264	$273.23	$273.25	$273.20
Purchase #3	$103.55	4.695%	$108.4117	$108.41	$108.40	$108.40
Purchase #4	$104.81	9.401%	$114.6632	$114.66	$114.65	$114.70
Purchase #5	$244.96	7.702%	$263.8268	$263.83	$263.85	$263.80
Purchase #6	$178.87	8.162%	$193.4694	$193.47	$193.45	$193.50
Purchase #7	$41.34	10.155%	$45.5381	$45.54	$45.55	$45.50
7 purchase totals =	$957.69		$1,039.5206	$1,039.53	$1,039.55	$1,039.50