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	$94.63	11.547%	$105.5569	$105.56	$105.55	$105.60
Purchase #2	$86.34	13.345%	$97.8621	$97.86	$97.85	$97.90
Purchase #3	$113.39	9.359%	$124.0022	$124.00	$124.00	$124.00
Purchase #4	$80.43	6.113%	$85.3467	$85.35	$85.35	$85.30
Purchase #5	$46.68	12.615%	$52.5687	$52.57	$52.55	$52.60
Purchase #6	$19.42	9.709%	$21.3055	$21.31	$21.30	$21.30
Purchase #7	$21.85	10.362%	$24.1141	$24.11	$24.10	$24.10
7 purchase totals =	$462.74		$510.7562	$510.76	$510.70	$510.80