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	$19.93	9.274%	$21.7783	$21.78	$21.80	$21.80
Purchase #2	$132.56	6.484%	$141.1552	$141.16	$141.15	$141.20
Purchase #3	$49.57	8.774%	$53.9193	$53.92	$53.90	$53.90
Purchase #4	$145.57	7.458%	$156.4266	$156.43	$156.45	$156.40
Purchase #5	$106.69	12.387%	$119.9057	$119.91	$119.90	$119.90
Purchase #6	$159.43	13.737%	$181.3309	$181.33	$181.35	$181.30
Purchase #7	$145.45	10.216%	$160.3092	$160.31	$160.30	$160.30
7 purchase totals =	$759.20		$834.8252	$834.84	$834.85	$834.80