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	$107.65	5.109%	$113.1498	$113.15	$113.15	$113.10
Purchase #2	$86.27	3.354%	$89.1635	$89.16	$89.15	$89.20
Purchase #3	$152.98	5.729%	$161.7442	$161.74	$161.75	$161.70
Purchase #4	$10.98	3.189%	$11.3302	$11.33	$11.35	$11.30
Purchase #5	$43.30	10.464%	$47.8309	$47.83	$47.85	$47.80
Purchase #6	$136.70	10.281%	$150.7541	$150.75	$150.75	$150.80
Purchase #7	$82.97	12.161%	$93.06	$93.06	$93.05	$93.10
7 purchase totals =	$620.85		$667.0327	$667.02	$667.05	$667.00