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	$15.69	12.226%	$17.6083	$17.61	$17.60	$17.60
Purchase #2	$189.80	4.503%	$198.3467	$198.35	$198.35	$198.30
Purchase #3	$25.82	13.752%	$29.3708	$29.37	$29.35	$29.40
Purchase #4	$114.70	5.114%	$120.5658	$120.57	$120.55	$120.60
Purchase #5	$173.97	6.604%	$185.459	$185.46	$185.45	$185.50
Purchase #6	$162.85	13.301%	$184.5107	$184.51	$184.50	$184.50
Purchase #7	$187.90	4.400%	$196.1676	$196.17	$196.15	$196.20
7 purchase totals =	$870.73		$932.0289	$932.04	$931.95	$932.10