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	$147.96	11.844%	$165.4844	$165.48	$165.50	$165.50
Purchase #2	$98.29	7.348%	$105.5123	$105.51	$105.50	$105.50
Purchase #3	$229.93	4.592%	$240.4884	$240.49	$240.50	$240.50
Purchase #4	$5.72	11.674%	$6.3878	$6.39	$6.40	$6.40
Purchase #5	$188.98	13.168%	$213.8649	$213.86	$213.85	$213.90
Purchase #6	$11.53	8.537%	$12.5143	$12.51	$12.50	$12.50
Purchase #7	$82.94	12.541%	$93.3415	$93.34	$93.35	$93.30
7 purchase totals =	$765.35		$837.5936	$837.58	$837.60	$837.60