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	$37.94	6.871%	$40.5469	$40.55	$40.55	$40.50
Purchase #2	$113.63	5.546%	$119.9319	$119.93	$119.95	$119.90
Purchase #3	$193.66	13.317%	$219.4497	$219.45	$219.45	$219.40
Purchase #4	$131.30	9.767%	$144.1241	$144.12	$144.10	$144.10
Purchase #5	$226.47	3.802%	$235.0804	$235.08	$235.10	$235.10
Purchase #6	$94.73	5.364%	$99.8113	$99.81	$99.80	$99.80
Purchase #7	$36.62	5.315%	$38.5664	$38.57	$38.55	$38.60
7 purchase totals =	$834.35		$897.5107	$897.51	$897.50	$897.40