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	$37.79	5.649%	$39.9248	$39.92	$39.90	$39.90
Purchase #2	$239.34	9.494%	$262.0629	$262.06	$262.05	$262.10
Purchase #3	$54.28	10.252%	$59.8448	$59.84	$59.85	$59.80
Purchase #4	$22.46	10.626%	$24.8466	$24.85	$24.85	$24.80
Purchase #5	$219.32	9.439%	$240.0216	$240.02	$240.00	$240.00
Purchase #6	$242.69	9.202%	$265.0223	$265.02	$265.00	$265.00
Purchase #7	$245.61	7.824%	$264.8265	$264.83	$264.85	$264.80
7 purchase totals =	$1,061.49		$1,156.5495	$1,156.54	$1,156.50	$1,156.40