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	$35.35	5.765%	$37.3879	$37.39	$37.40	$37.40
Purchase #2	$234.68	3.703%	$243.3702	$243.37	$243.35	$243.40
Purchase #3	$149.95	4.262%	$156.3409	$156.34	$156.35	$156.30
Purchase #4	$31.51	3.160%	$32.5057	$32.51	$32.50	$32.50
Purchase #5	$28.41	7.704%	$30.5987	$30.60	$30.60	$30.60
Purchase #6	$92.74	8.440%	$100.5673	$100.57	$100.55	$100.60
Purchase #7	$200.33	7.863%	$216.0819	$216.08	$216.10	$216.10
7 purchase totals =	$772.97		$816.8526	$816.86	$816.85	$816.90