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	$225.84	6.411%	$240.3186	$240.32	$240.30	$240.30
Purchase #2	$93.60	9.239%	$102.2477	$102.25	$102.25	$102.20
Purchase #3	$142.81	5.740%	$151.0073	$151.01	$151.00	$151.00
Purchase #4	$213.57	8.385%	$231.4778	$231.48	$231.50	$231.50
Purchase #5	$24.59	11.258%	$27.3583	$27.36	$27.35	$27.40
Purchase #6	$80.73	12.599%	$90.9012	$90.90	$90.90	$90.90
Purchase #7	$168.43	6.674%	$179.671	$179.67	$179.65	$179.70
7 purchase totals =	$949.57		$1,022.9819	$1,022.99	$1,022.95	$1,023.00