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	$140.57	8.740%	$152.8558	$152.86	$152.85	$152.90
Purchase #2	$176.64	6.129%	$187.4663	$187.47	$187.45	$187.50
Purchase #3	$54.53	9.236%	$59.5664	$59.57	$59.55	$59.60
Purchase #4	$12.34	4.220%	$12.8607	$12.86	$12.85	$12.90
Purchase #5	$149.65	4.347%	$156.1553	$156.16	$156.15	$156.20
Purchase #6	$42.90	8.599%	$46.589	$46.59	$46.60	$46.60
Purchase #7	$243.34	13.110%	$275.2419	$275.24	$275.25	$275.20
7 purchase totals =	$819.97		$890.7354	$890.75	$890.70	$890.90